I found this while roll hunting. I'm not sure how to describe this error, but here is a picture:
How much does anyone think it's worth? eBay it and find out?
"Specie is the most perfect medium because it will preserve its own level; because, having intrinsic and universal value, it can never die in our hands, and it is the surest resource of reliance in time of war." -Thomas Jefferson
Nice find. It's probably a grease fill error (like daviscfad said), especially if the reverse is clearly defined. You might be able to get a Buck for it, but it looks pretty beat up. I'd just keep it with my personal "Geez this is Neat" collection.