Is this a mint error? Thoughts on how it got there? Any value besides $.50? The coin is part of the 2005 United States Mint Proof Set. The marking is on the coin, not the plastic container. More up close picture:
I don't think it's a 6 at all. It is a 9 that is upside down. It appears to be a hit from something. I think it is considered damage.
It looks like a strikethrough, possibly caused by a small piece of wire or metal sliver. It's kind of cool that it just happened to form the shape of a "6". It's hard to place a set value on something like this. Some people may like it simply as a conversation piece, Some other person might pay a small premium to add it to his "Strikethrough Errors", but if two or more people want it, there is no telling what the final price might be. Chris
