Besides the curl on the 9 which goes around more, there is the sharp chiseled bottom of the 9 stem, or the blunt bottom.
LD, although I admit that one can fool the uninitiated. By the way, I'm still looking for the SD proof, but I have a honey of a circ. strike one - NGC MS66RD, plucked from a BU roll I paid 3 bucks for.