The single letter following a verse

What is the significance of the Single letter, S or P standing alone following a verse in the Hebrew Bible?

Here are some examples I have come across so far. In some books the letter might be seen as marking sections, but this is clearly not the case. In Leviticus, the first chapter has S-P- then S on verses 9, 13, and 17. They mark a repeated word pair. In Deuteronomy the markings are on verses 14, 68 and 69. In neither case could these be defining sections for reading. In Lamentations chapters 1, 3, and 4, there's a letter on every verse (or every third verse for chapter 3), but none in chapters 1 or 5. The S reminds me of Selah. The P, I don't know. The verses are significant - maybe just stop, pause and ponder.

The P occurs 452 times in my data to date. The S occurs 165 times. That's in a little over 6000 verses.

Genesis 2
וַיְבָ֤רֶךְ אֱלֹהִים֙ אֶת־י֣וֹם הַשְּׁבִיעִ֔י וַיְקַדֵּ֖שׁ אֹת֑וֹ כִּ֣י ב֤וֹ שָׁבַת֙ מִכָּל־מְלַאכְתּ֔וֹ אֲשֶׁר־בָּרָ֥א אֱלֹהִ֖ים לַעֲשֽׂוֹת פ	3	And God blessed the seventh day and made it holy. For on it he ceased from all his affairs that God created for construction. P
Leviticus 1
וְקִרְבּ֥וֹ וּכְרָעָ֖יו יִרְחַ֣ץ בַּמָּ֑יִם וְהִקְטִ֨יר הַכֹּהֵ֤ן אֶת־הַכֹּל֙ הַמִּזְבֵּ֔חָה עֹלָ֛ה אִשֵּׁ֥ה רֵֽיחַ־נִיח֖וֹחַ לַֽיהוָֽה ס	9	But its entrails and its limbs he will wash in water. And the priest will cause it all to burn with smoke toward the altar, a burnt offering by fire, an appeasing smell for Yahweh. S
וְהַקֶּ֥רֶב וְהַכְּרָעַ֖יִם יִרְחַ֣ץ בַּמָּ֑יִם וְהִקְרִ֨יב הַכֹּהֵ֤ן אֶת־הַכֹּל֙ וְהִקְטִ֣יר הַמִּזְבֵּ֔חָה עֹלָ֣ה ה֗וּא אִשֵּׁ֛ה רֵ֥יחַ נִיחֹ֖חַ לַיהוָֽה פ	13	But its entrails and its limbs he will wash in water. And the priest will bring it all near and will cause it to burn with smoke toward the altar. It is a burnt offering by fire, an appeasing smell for Yahweh. P
וְשִׁסַּ֨ע אֹת֣וֹ בִכְנָפָיו֮ לֹ֣א יַבְדִּיל֒ וְהִקְטִ֨יר אֹת֤וֹ הַכֹּהֵן֙ הַמִּזְבֵּ֔חָה עַל־הָעֵצִ֖ים אֲשֶׁ֣ר עַל־הָאֵ֑שׁ עֹלָ֣ה ה֗וּא אִשֵּׁ֛ה רֵ֥יחַ נִיחֹ֖חַ לַיהוָֽה ס	17	And he will spread it out by its wings. He will not differentiate. And the priest will cause it to burn with smoke toward the altar on the trees that are on the fire. It is a burnt offering made by fire, an appeasing smell for Yahweh. S
Deuteronomy 28
וְלֹ֣א תָס֗וּר מִכָּל־הַדְּבָרִים֙ אֲשֶׁ֨ר אָנֹכִ֜י מְצַוֶּ֥ה אֶתְכֶ֛ם הַיּ֖וֹם יָמִ֣ין וּשְׂמֹ֑אול לָלֶ֗כֶת אַחֲרֵ֛י אֱלֹהִ֥ים אֲחֵרִ֖ים לְעָבְדָֽם ס	14	And you will not turn aside from all the things that I myself have commanded you today to the right hand or to the left to walk after other gods to serve them. S
וֶֽהֱשִֽׁיבְךָ֨‬ יְהוָ֥ה ׀ מִצְרַיִם֮ בָּאֳנִיּוֹת֒ בַּדֶּ֙רֶךְ֙ אֲשֶׁ֣ר אָמַ֣רְתִּֽי לְךָ֔ לֹא־תֹסִ֥יף ע֖וֹד לִרְאֹתָ֑הּ וְהִתְמַכַּרְתֶּ֨ם שָׁ֧ם לְאֹיְבֶ֛יךָ לַעֲבָדִ֥ים וְלִשְׁפָח֖וֹת וְאֵ֥ין קֹנֶֽה ס	68	And Yahweh will have you return to Egypt by ship in the way that I said to you, You will no longer again see it. And you will be on sale there to your enemies as servants and as handmaidens and there is no one to purchase. S
אֵלֶּה֩ דִבְרֵ֨י הַבְּרִ֜ית אֲ‍ֽשֶׁר־צִוָּ֧ה יְהוָ֣ה אֶת־מֹשֶׁ֗ה לִכְרֹ֛ת אֶת־בְּנֵ֥י יִשְׂרָאֵ֖ל בְּאֶ֣רֶץ מוֹאָ֑ב מִלְּבַ֣ד הַבְּרִ֔ית אֲשֶׁר־כָּרַ֥ת אִתָּ֖ם בְּחֹרֵֽב פ	69	These are the words of the covenant which Yahweh commanded Moses to cut with the children of Israel in the land of Moab, besides the covenant which he cut with them in Horeb. P
1 Samuel 17
וַיֹּ֨אמֶר שָׁא֜וּל אֶל־דָּוִ֗ד לֹ֤א תוּכַל֙ לָלֶ֙כֶת֙ אֶל־הַפְּלִשְׁתִּ֣י הַזֶּ֔ה לְהִלָּחֵ֖ם עִמּ֑וֹ כִּֽי־נַ֣עַר אַ֔תָּה וְה֛וּא אִ֥ישׁ מִלְחָמָ֖ה מִנְּעֻרָֽיו ס	33	And Saul said to David, You cannot go to this Philistine to fight with him for a youth are you and he a man of war from his youth. S
גַּ֧ם אֶֽת־הָאֲרִ֛י גַּם־הַדּ֖וֹב הִכָּ֣ה עַבְדֶּ֑ךָ וְֽ֠הָיָה הַפְּלִשְׁתִּ֨י הֶעָרֵ֤ל הַזֶּה֙ כְּאַחַ֣ד מֵהֶ֔ם כִּ֣י חֵרֵ֔ף מַעַרְכֹ֖ת אֱלֹהִ֥ים חַיִּֽים ס	36	Even the lion even the bear your servant will strike, so this fore-skinned Philistine will be as one with them for he has reproached the ranks of the living God. S
וַיֹּ֥אמֶר הַפְּלִשְׁתִּ֖י אֶל־דָּוִ֑ד לְכָ֣ה אֵלַ֔י וְאֶתְּנָה֙ אֶת־בְּשָׂ֣רְךָ֔ לְע֥וֹף הַשָּׁמַ֖יִם וּלְבֶהֱמַ֥ת הַשָּׂדֶֽה ס	44	And the Philistine said to David, Come on to me and I will give your flesh to the fowl of the heavens and the beasts of the field. S
Jonah 2
וַאֲנִ֗י בְּק֤וֹל תּוֹדָה֙ אֶזְבְּחָה־לָּ֔ךְ אֲשֶׁ֥ר נָדַ֖רְתִּי אֲשַׁלֵּ֑מָה יְשׁוּעָ֖תָה לַיהוָֽה ס	10	So I in a voice of thanksgiving will offer you what I have vowed to repay. Salvation to Yahweh belongs. S
וַיֹּ֥אמֶר יְהוָ֖ה לַדָּ֑ג וַיָּקֵ֥א אֶת־יוֹנָ֖ה אֶל־הַיַּבָּשָֽׁה פ	11	And Yahweh talked to the fish, and it vomited Jonah onto the dry land. P
Jonah 4
וְעַתָּ֣ה יְהוָ֔ה קַח־נָ֥א אֶת־נַפְשִׁ֖י מִמֶּ֑נִּי כִּ֛י ט֥וֹב מוֹתִ֖י מֵחַיָּֽי ס	3	And now Yahweh take please my being from me, for death is good compared with my life. S
Zephaniah 1
וּפָקַדְתִּ֗י עַ֧ל כָּל־הַדּוֹלֵ֛ג עַל־הַמִּפְתָּ֖ן בַּיּ֣וֹם הַה֑וּא הַֽמְמַלְאִ֛ים בֵּ֥ית אֲדֹנֵיהֶ֖ם חָמָ֥ס וּמִרְמָֽה ס	9	and I will visit all who leap over the adder on that day, those filling their master's house with violence and deceit. S
גַּם־כַּסְפָּ֨ם גַּם־זְהָבָ֜ם לֹֽא־יוּכַ֣ל לְהַצִּילָ֗ם בְּיוֹם֙ עֶבְרַ֣ת יְהוָ֔ה וּבְאֵשׁ֙ קִנְאָת֔וֹ תֵּאָכֵ֖ל כָּל־הָאָ֑רֶץ כִּֽי־כָלָ֤ה אַךְ־נִבְהָלָה֙ יַֽעֲשֶׂ֔ה אֵ֥ת כָּל־יֹשְׁבֵ֖י הָאָֽרֶץ ס	18	Even their silver, even their gold will not be able to deliver them in the day of Yahweh's fury, but in the fire of his jealousy all the land will be devoured. For surely, a consuming vexation he will make for all those inhabiting the land. S
Zephaniah 2
כִּ֤י עַזָּה֙ עֲזוּבָ֣ה תִֽהְיֶ֔ה וְאַשְׁקְל֖וֹן לִשְׁמָמָ֑ה אַשְׁדּ֗וֹד בַּֽצָּהֳרַ֙יִם֙ יְגָ֣רְשׁ֔וּהָ וְעֶקְר֖וֹן תֵּעָקֵֽר ס	4	For Gaza will be forsaken and Ashkelon, desolate. Ashdod at noon they will expel, and Akron. S
זֹ֠את הָעִ֤יר הָעַלִּיזָה֙ הַיּוֹשֶׁ֣בֶת לָבֶ֔טַח הָאֹֽמְרָה֙ בִּלְבָבָ֔הּ אֲנִ֖י וְאַפְסִ֣י ע֑וֹד אֵ֣יךְ ׀ הָיְתָ֣ה לְשַׁמָּ֗ה מַרְבֵּץ֙ לַֽחַיָּ֔ה כֹּ֚ל עוֹבֵ֣ר עָלֶ֔יהָ יִשְׁרֹ֖ק יָנִ֥יעַ יָדֽוֹ ס	15	This is the exultant city, the confident inhabitant. She says in her heart, I am and my ends continue. How she has become desolated, for the animals to recline. All who pass by her will hiss and waggle their hand. S
Zephaniah 3
שְׁאֵרִ֨ית יִשְׂרָאֵ֜ל לֹֽא־יַעֲשׂ֤וּ עַוְלָה֙ וְלֹא־יְדַבְּר֣וּ כָזָ֔ב וְלֹֽא־יִמָּצֵ֥א בְּפִיהֶ֖ם לְשׁ֣וֹן תַּרְמִ֑ית כִּֽי־הֵ֛מָּה יִרְע֥וּ וְרָבְצ֖וּ וְאֵ֥ין מַחֲרִֽיד ס	13	The residue of Israel will not do injustice and will not speak a lie and in their mouths a deceitful tongue will not be found, for they themselves will pasture and recline and without apprehensiveness. S
Haggai 1
וָאֶקְרָ֨א חֹ֜רֶב עַל־הָאָ֣רֶץ וְעַל־הֶהָרִ֗ים וְעַל־הַדָּגָן֙ וְעַל־הַתִּיר֣וֹשׁ וְעַל־הַיִּצְהָ֔ר וְעַ֛ל אֲשֶׁ֥ר תּוֹצִ֖יא הָאֲדָמָ֑ה וְעַל־הָֽאָדָם֙ וְעַל־הַבְּהֵמָ֔ה וְעַ֖ל כָּל־יְגִ֥יעַ כַּפָּֽיִם ס	11	So I called a desert onto the earth and onto the hills and onto the grain and onto the new wine and onto the fresh oil and onto that which emerges from the ground and onto the human and onto the beast and onto all the labour of their palms. S
וַיְהִ֡י כִּ֣י הִקִּיפֽוּ֩ יְמֵ֨י הַמִּשְׁתֶּ֜ה וַיִּשְׁלַ֧ח אִיּ֣וֹב וַֽיְקַדְּשֵׁ֗ם וְהִשְׁכִּ֣ים בַּבֹּקֶר֮ וְהֶעֱלָ֣ה עֹלוֹת֮ מִסְפַּ֣ר כֻּלָּם֒ כִּ֚י אָמַ֣ר אִיּ֔וֹב אוּלַי֙ חָטְא֣וּ בָנַ֔י וּבֵרֲכ֥וּ אֱלֹהִ֖ים בִּלְבָבָ֑ם כָּ֛כָה יַעֲשֶׂ֥ה אִיּ֖וֹב כָּל־הַיָּמִֽים פ	5	And it would be that after the striking off of party days, Job would send and sanctify them rising early in the morning to offer up burnt offerings for all of them for Job said, Perhaps my sons have sinned and blessed God in their hearts. Thus did Job every one of the days. P
בְּכָל־זֹ֖את לֹא־חָטָ֣א אִיּ֑וֹב וְלֹא־נָתַ֥ן תִּפְלָ֖ה לֵאלֹהִֽים פ	22	In all this Job did not sin nor did he assign fickleness to God. P
Job 2
וַיֹּ֣אמֶר אֵלֶ֗יהָ כְּדַבֵּ֞ר אַחַ֤ת הַנְּבָלוֹת֙ תְּדַבֵּ֔רִי גַּ֣ם אֶת־הַטּ֗וֹב נְקַבֵּל֙ מֵאֵ֣ת הָאֱלֹהִ֔ים וְאֶת־הָרָ֖ע לֹ֣א נְקַבֵּ֑ל בְּכָל־זֹ֛את לֹא־חָטָ֥א אִיּ֖וֹב בִּשְׂפָתָֽיו פ	10	But he said to her, You speak as one of the foolish women might speak. Indeed, will we undergo the good from God and not undergo the evil? In all this Job did not sin with his lips. P
Job 3
לֹ֤א שָׁלַ֨וְתִּי ׀ וְלֹ֖א שָׁקַ֥טְתִּי וְֽלֹא־נָ֗חְתִּי וַיָּ֥בֹא רֹֽגֶז פ	26	I have no ease nor am I quiet nor am I at rest and shuddering has come. P
Job 7
וּמֶ֤ה ׀ לֹא־תִשָּׂ֣א פִשְׁעִי֮ וְתַעֲבִ֪יר אֶת־עֲוֺ֫נִ֥י כִּֽי־עַ֭תָּה לֶעָפָ֣ר אֶשְׁכָּ֑ב וְשִׁ֖חֲרְתַּ֣נִי וְאֵינֶֽנִּי פ	21	And why do you not assume liability for my transgression and go beyond my iniquity? For now in the dust I will lie down and early you will seek me and there is no me. P
Job 28
מִ֭בְּכִי נְהָר֣וֹת חִבֵּ֑שׁ וְ֝תַעֲלֻמָ֗הּ‬ יֹ֣צִא אֽוֹר פ	11	From weeping he binds rivers, and obscure things he brings to light. P
לֹֽא־יַ֭עַרְכֶנָּה פִּטְדַת־כּ֑וּשׁ בְּכֶ֥תֶם טָ֝ה֗וֹר לֹ֣א תְסֻלֶּֽה פ	19	She is not arranged by the topaz of Cush nor in fine lustrous gold is she suspended. P
וַיֹּ֤אמֶר ׀ לָֽאָדָ֗ם הֵ֤ן יִרְאַ֣ת אֲ֭דֹנָי הִ֣יא חָכְמָ֑ה וְס֖וּר מֵרָ֣ע בִּינָֽה ס	28	And he said to the human, Indeed, the fear of the Lord, that is wisdom, and to depart from evil is discernment. S
Proverbs 8
לְהַנְחִ֖יל אֹהֲבַ֥י ׀ יֵ֑שׁ וְאֹצְרֹ֖תֵיהֶ֣ם אֲמַלֵּֽא פ	21	to make those loving me inherit what is, so I fill their treasuries. P
מְ֭שַׂחֶקֶת בְּתֵבֵ֣ל אַרְצ֑וֹ וְ֝שַׁעֲשֻׁעַ֗י אֶת־בְּנֵ֥י אָדָֽם פ	31	gamboling in the world of his earth, reveling with the children of humanity. P
וְֽ֭חֹטְאִי חֹמֵ֣ס נַפְשׁ֑וֹ כָּל־מְ֝שַׂנְאַ֗י אָ֣הֲבוּ מָֽוֶת פ	36	But who sins against me does itself violence. All who hate me love death. P
Song 1
מָשְׁכֵ֖נִי אַחֲרֶ֣יךָ נָּר֑וּצָה הֱבִיאַ֨נִי הַמֶּ֜לֶךְ חֲדָרָ֗יו נָגִ֤ילָה וְנִשְׂמְחָה֙ בָּ֔ךְ נַזְכִּ֤ירָה דֹדֶ֙יךָ֙ מִיַּ֔יִן מֵישָׁרִ֖ים אֲהֵבֽוּךָ ס	4	Draw me out. After you we will run. The king brought me into his rooms. We will rejoice and we will be glad in you. We will mention your caresses more than wine. The upright have loved you. S
אִם־לֹ֤א תֵדְעִי֙ לָ֔ךְ הַיָּפָ֖ה בַּנָּשִׁ֑ים צְֽאִי־לָ֞ךְ בְּעִקְבֵ֣י הַצֹּ֗אן וּרְעִי֙ אֶת־גְּדִיֹּתַ֔יִךְ עַ֖ל מִשְׁכְּנ֥וֹת הָרֹעִֽים ס	8	If you do not know for yourself, beautiful among women, go out for yourself in the footsteps of the flock and graze your kids by the shepherds' dwellings. S
אֶשְׁכֹּ֨ל הַכֹּ֤פֶר ׀ דּוֹדִי֙ לִ֔י בְּכַרְמֵ֖י עֵ֥ין גֶּֽדִי ס	14	A cluster of camphire is my beloved to me in the vineyards of Ein Gedi. S
Song 2
יוֹנָתִ֞י בְּחַגְוֵ֣י הַסֶּ֗לַע בְּסֵ֙תֶר֙ הַמַּדְרֵגָ֔ה הַרְאִ֙ינִי֙ אֶתּ־מַרְאַ֔יִךְ הַשְׁמִיעִ֖ינִי אֶת־קוֹלֵ֑ךְ כִּי־קוֹלֵ֥ךְ עָרֵ֖ב וּמַרְאֵ֥יךְ נָאוֶֽה ס	14	My dove, in the clefts of the cliff, in the secret steep place, let me see your appearance, and let me hear your tone, for your tone is sweet and your appearance is lovely. S
עַ֤ד שֶׁיָּפ֙וּחַ֙ הַיּ֔וֹם וְנָ֖סוּ הַצְּלָלִ֑ים סֹב֩ דְּמֵה־לְךָ֨ דוֹדִ֜י לִצְבִ֗י א֛וֹ לְעֹ֥פֶר הָאַיָּלִ֖ים עַל־הָ֥רֵי בָֽתֶר ס	17	Till the day dawns and the shadows withdraw, surround, be like, you, my beloved, the gazelle or the faun of the hart upon the rugged mountains. S
Song 3
צְאֶ֧ינָה ׀ וּֽרְאֶ֛ינָה בְּנ֥וֹת צִיּ֖וֹן בַּמֶּ֣לֶךְ שְׁלֹמֹ֑ה בָּעֲטָרָ֗ה שֶׁעִטְּרָה־לּ֤וֹ אִמּוֹ֙ בְּי֣וֹם חֲתֻנָּת֔וֹ וּבְי֖וֹם שִׂמְחַ֥ת לִבּֽוֹ ס	11	Go forth and see, daughters of Zion, on the king Solomon, the crown that his mother crowned him with on the day he is bridegroom and on the day of the gladness in his heart. S
Ruth 4
וַתִּקְרֶאנָה֩ ל֨וֹ הַשְּׁכֵנ֥וֹת שֵׁם֙ לֵאמֹ֔ר יֻלַּד־בֵּ֖ן לְנָעֳמִ֑י וַתִּקְרֶ֤אנָֽה שְׁמוֹ֙ עוֹבֵ֔ד ה֥וּא אֲבִי־יִשַׁ֖י אֲבִ֥י דָוִֽד פ	17	And the neighbours called him a name saying, A son is born to Naomi. And they called his name Obed. He is the father of Jesse, the father of David. P
Qohelet 9
כֹּ֠ל אֲשֶׁ֨ר תִּמְצָ֧א יָֽדְךָ֛ לַעֲשׂ֥וֹת בְּכֹחֲךָ֖ עֲשֵׂ֑ה כִּי֩ אֵ֨ין מַעֲשֶׂ֤ה וְחֶשְׁבּוֹן֙ וְדַ֣עַת וְחָכְמָ֔ה בִּשְׁא֕וֹל אֲשֶׁ֥ר אַתָּ֖ה הֹלֵ֥ךְ שָֽׁמָּה ס	10	All that you find to your hand to do, in your power do, for there is no deed or reason or knowledge or shrewdness in the grave thereto where you yourself are going. S