I have seen what I think you are describing often. I believe it is caused when the mintmark is punched into the working die. Some metal is displaced and pushed upward on the die and thus creates a sunken area around the mm on the coins.
In Memory of Crazyb0 12-26-1951 to 7-27-2020
In Memory of Tootallious 3-31-1964 to 4-15-2020
In Memory of T-BOP 10-12-1949 to 1-19-2024
In Memory of Tootallious 3-31-1964 to 4-15-2020
In Memory of T-BOP 10-12-1949 to 1-19-2024

























