1875-S 20 Cent Greaser

I can't see it as "normal" wear, at one particular area at the rim when the rest of the circumference isn't nearly as worn. The transition between "wear" and "not wear" is too abrupt. Grease is a strong possibility.

Grease is a possibility. Unfortunately enlarging the picture does not help. Makes the area look badly photoshopped (deliberately blurred, not saying it has been just that it looks that way.). One thing I was wondering was about the possibility that the coin was altered contemporaneously. The size and design was close enough to that of a quarter that supposedly some people would alter the reverse and pass them as quarters.