Just a post from a disgruntled person claiming they have one. See this post: https://www.cointalk.com/threads/1966-dime-with-5-on-cheek.386618/
I can't believer this nonsense has gone on for 7 pages. As many have already said this is PMD (post mint damage) nothing more. If you see a crude 5, fine. It's worth 10c on the market, but it may mean more to you. Selling on e-Bay may just get you someone else ignorant of the minting process. Have at it, just don't misrepresent it as an error by the U.S. Mint.
When Fred said it was a lint mark on the die he didn't explain far enough. The lint mark is the result of a strike through in the hubbing of the die. The lint was on the die blank and the hub forced it into the die face (incuse mark into the die), so the result on the struck coin is the raised lint mark "5", and it repeats on other coins struck from that die. Which is why there is more than one of them.