The Mechon-Mamre cantillation is missing the final ornament. If one is going to see these marks as punctuation, I suppose one might frequently miss the point. The Max Letteris edition clearly has the closing ornament:
לָ֠כֵן יִתֵּ֨ן אֲדֹנָ֥י ה֛וּא לָכֶ֖ם א֑וֹת
הִנֵּ֣ה הָֽעַלְמָ֗ה הָרָה֙ וְיֹלֶ֣דֶת בֵּ֔ן
וְקָרָ֥את שְׁמ֖וֹ עִמָּ֥נוּ֩ אֵֽל
(therefore the Lord himself will give you(pl) a sign.
Behold, the young woman is with child and will birth a son,
and she will call his name God-with-us.)
Note how the ornaments (above the letters) and notes (below the letters) are related to the interpretation of the text. Could we, I wonder, do such a thing? Let music interpret the text? The melody right in the middle of this inclusio under veyelodet ben - and will bear a son, is the same as that for the beginning of David's lament over Absalom in 2 Samuel 19:1 (18:33). This melody also occurs to open the song in Isaiah 26:1 - I wonder if it is a signal, the music recognizing implicitly the sorrow of the death of a child. In Isaiah 26 it is the impending doom over Israel.
This year I hope to read Isaiah in detail, using both Hebrew and Greek texts. I will keep my ears open for these aspects of 'punctuation' in the marks of taste in the Hebrew text.