It may be, but I have not seen any such pottery in any search I have done, so it isn't a common symbol used or on a significant piece (i.e. the bronze head for Akkad). So, at this point, I can't give any better explanation than the one I have brought so far. Friaxis sometimes takes a bit of artistic license with these symbols, but I have found they always at least relate to something significant. With this one, I don't know if they are using an actual piece or stylizing it based on a the general designs. I can not find anything remotely close to it and particularly nothing with any cultural historical significance. If someone would like to provide images of the pottery they used I could possibly find the meaning of the symbols used or more about the uniqueness that the style of pottery may hold within the Nubian culture.