Sa (cuneiform)
The cuneiform sa sign is a less common-use sign of the Epic of Gilgamesh, the 1350 BC Amarna letters, and other cuneiform texts. It also has a sumerogrammic usage for SA in the Epic of Gilgamesh. The structure of the cuneiform sign is similar to, Ir (cuneiform), .

The "sa" sign has the syllabic usage for sa, and a sumerogram usage for SA. Alphabetically "sa" can be used for s ("s" can be interchanged with any "z"); and "sa" can be used for a. In Akkadian, all 4 vowels, a, e, i, u are interchangeable with each other. 

SA in the Epic of Gilgamesh is a logogram for Akkadian "Šer'ānu", translated as: "muscle, sinew".

Epic of Gilgamesh usage
The sa sign usage in the Epic of Gilgamesh is as follows: sa-(89 times); and SA-(2).