The discoloration forming around the outside of the mintmark tells me there is something going on beneath the surface. This will probably end up as some kind of rot eventually. The copper layer was probably too thin in this spot. I can't see any splitting but I fear the zinc is pushing up there. All it takes is the smallest pinhole you cannot see to start the process. Also, look on the left side of the mint mark where there appears to be "doubling". The whole thing is going in the wrong direction to be a RPM. JMHO.
