Good evening my friend
Those are Mint Marks
Last year I purchased a Silver Strike guide book and it gives some great insight to the hobby
Here is a short list of the mints where our beloved strikes are struck
CC — continental coin Corp
G — Global minting
GDC — Green Duck Corporation
S — Sunshine Mint
TPM — The Perth Mint
LM Letcher Mint

Just like a P, D, Or S on United States coins this is the mint in which the coin was struck

Enjoy

Dean
SS-1977