Unto 1967 Proof Jefferson Proof Nickels were minted in Philadelphia with no mint marking. 1968 onwards were minted S at the San Francisco Mint.
I buy many coins in lots and to keep track of them I label them as so in lots to know how much I paid for it, or if I found it metal detecting etc...
This coin does show its full steps but they are not hard struck like many are. And this coin has a lot of toning spots on it. Decent coin mid grade rating of say a PF67-68