I saw this coin and thought that the mintmark nicely demonstrated the difference between a digamma- ϛ and the letter "S". This digamma symbol is Greek and was used on some Roman coins to represent the sixth workshop. It is commonly referred to as an "S", which it resembles, sometimes it is hard to even make a distinction. On the coin pictured, the mintmark is CONSϛ - sixth workshop of Constantinople.
I generally call it an "S" in my descriptions also...maybe I should make more of an effort to be correct, rather than perpetuate confusion!