The cuneiform sign šum is a common-use sign of the Amarna letters, the Epic of Gilgamesh, and other cuneiform texts (for example Hittite texts).
Linguistically, it has a syllabic usage for šum, as well as for tag, tak, and taq. It can also be used alphabetically for š, m, t, g, k, or q, and also as a replacement for the four vowels, of a, or e, or i, or u.
The šum sign usage in the Epic of Gilgamesh is as follows: (šum, 34 times, tag, 2, tak, 23, and taq, 7 times).[1]
A common usage of the šum cuneiform in the Amarna letters is for the Akkadian word šumma,[2], for English if. In the letters the strife with the Habiru, taking over cities, (city-states), the reference is, "If the pharaoh doesn't send the archer force, our town is lost!".