@kim moster Welcome to CoinTalk. Unfortunately it is not a Mint Error. As stated by the others it's a counterstamp added to the Nickel after it left the US Mint. Here is one I once made myself with the letters P and R
I went and looked on Etsy to see perhaps if there was one for sale there with the description: "Super rare American Nickel, the Philadelphia mint ran out of mint marks for their nickels, so they had to start hand punching them on the reverse of each nickel minted. $50,000 USD (Plus Shipping)."
I can’t believe the ridiculous crap you see on Etsy and Ebay with astronomical prices. Always good for a laugh.