The letters haven't been punch into a die since 1908. Since then they are all part of the hub that passes the information to the dies. The mint marks were added until 1989. Then in 1990 the design for the mint mark was also part of the hubs design. So there is not chance this is a 5. It was an 'S' then was altered by a coin hit. The coin has been in the wild for over 46 years. Its bound to take a klunker or two.