Šu

The cuneiform šu sign is a common, multi-use syllabic and alphabetic sign for šu, š, and u; it has a subsidiary usage for syllabic qat; it also has a majuscule- Sumerogram usage for ŠU, for Akkadian language "qātu", the word for "hand". The cuneiform character šu is shaped like a human hand and was created late 4th millennium BC or early 3rd millennium BC.
The scribal usage of a sign allows for any of the 4 vowels, a, e, i, u to be interchangeable; thus a usage for syllabic qat could conceivably be used for the following : q, a, or t; also ka, qa, ad, at.
The šu sign is quite common in the Amarna letters and the Epic of Gilgamesh as follows: qat-, šu-, ŠU-.