The cuneiform sign ṣur, is a common-use sign of the Amarna letters, the Epic of Gilgamesh, and other cuneiform texts (for example Hittite texts).
Linguistically, it has the alphabetical usage in texts for ṣ, or z; also r; for vowels, u, or as a replacement for the other three vowels, "a", "e", or "i".
The ṣur sign usage in the Epic of Gilgamesh is as follows: (ṣur, 6 times, zur, 1 time, and AMAR, 1 time.[1]