The cuneiform sign for the syllable ab also represents that for ap, or the vowel and consonant usages of a, b, or p: in the Akkadian language "b" is unaspirated, formed with the lips, and "p" is aspir
Mesopotamian tablet for Sin-Kashid. Line 3, second character, ab. (Note that the second pair of horizontals angle up, and down, to the large vertical stroke anchoring the right of the "ab" sign.)
Ayyab's letter to Pharaoh, Amarna letter EA 364. His name is spelled in (line 2)--"um-ma A-iYa-aB, "...message (speaking), Ayyab..." (Note, for ab, the second pair of horizontals are at different angles.)