Did it say in the game at all? Besides the obsuce
"There is only one reference that I have found to the #1 tattoo, and that's when Cloud is in Corel, and the man sitting outside the shack says that he saw a man in a black cape with a #1 tattoo on his arm. What makes me doubt that this Black Cape with the #1 tattoo is Sephiroth, is 1) Sephiroth's clothing is long-sleeved, and he is often seen wearing gloves. If this is the case, how did the man see a tattoo on Sephiroth's arm? "