Ṣur (cuneiform)
The cuneiform sign ṣur, is a common-use sign of the Amarna letters, the Epic of Gilgamesh, and other cuneiform 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".