The cuneiform sign at, is a common-use sign of the Amarna letters, the Epic of Gilgamesh, and other cuneiform texts (for example Hittite texts). It has secondary uses in the Amarna letters for "ad".
Linguistically, it has the alphabetical usage in texts for a, (also the 4 vowels, a, e, i, u), and t, and d.
The at sign usage in the Epic of Gilgamesh is as follows: (ad, 17 times, at, 107, aṭ, 15, and AD, 15 times).[1]