The cuneiformab, and ap sign, (in the Akkadian language world, 'b' is unaspirated, formed with the lips, and 'p' is "aspirated"-(aspirated consonant, with the breath)) is the cuneiform sign used for the syllables ab, or ap, or the vowel and consonant usages of a, b, or p. In the Akkadian language b-and-p are interchangeable; also in cuneiform texts, any vowel of the a, e, i, u (no "o" in Akkadian) can be interchanged with another. Also for the 'ab/ap' sign, there is a capital letter (majuscule) usage as a sumerogram, found in the Epic of Gilgamesh for AB, Akkadian language for šību, "elder".
In the corpus of the Amarna letters, which is another common use place for 'ab/ap', the name of some of the authors of letters to the Pharaoh, are for example Labaya, and Ayyab. In both cases the use is syllabic for ab.
The usage numbers for the "ab" cuneiform sign in the twelve, Tablets I-XII, of the Epic of Gilgamesh, are as follows: ab-(11), ap-(28), and sumerogram AB-(12); for "šību", Akkadian language for elder, only two spellings use "AB"; six other spelliings of "šību" are syllabic/alphabetic.
Rainey, 1970. El Amarna Tablets, 359-379,Anson F. Rainey, (AOAT 8, Alter Orient Altes Testament 8, Kevelaer and Neukirchen -Vluyen), 1970, 107 pages.
Ayyab's letter to Pharaoh, Amarna letter EA 364. His name is spelled in (line 2)--"um-maA-iYa-aB, "...message (speaking), Ayyab..."
(Note, for ab, the second pair of horizontals are at different angles.)