Mintmark, Privy Mark, and Counterstamp Coins
The term mintmark refers to a mark on the original die indicating the location where that coin was struck.
Pre-struck coins that are subsequently modified by the Mint using a metal punch on a mobile press prior to issue. A counterstamp can be identified as a symbol surrounded by a small circle.
Struck using a die that has been modified to include a letter or symbol commemorating a special release or event. In order to clearly identify these coins, the privy mark will consist of a letter or symbol with a square surround.