Over Mint Marks (OMM's) occur when the mint either repurposes a die or makes a mistake. The mint will eventually have two different mint marks on one working die. The process was to place one mint mark over the top of another. In some instances this was a D over an S, an S over a D, an O over a CC or other such combinations. Another subcategory here is the use of Double Mint Marks (DMM's). This occurred when two mint marks were added in different areas of the coin and no attempt was done to cover them up. In this forum please feel free to ask questions or post a comment on Over Mint Mark coins and Double Mint Mark coins.