RPM, also known as an Over Mint Mark, is a die variety that features an over-punched mint mark. These are common in many United States coinage series, but not all.
Some types of RPM are very rare. Examples include the 1909-S Lincoln Wheat Penny and the 1958-D Washington quarter. If you’re interested in collecting these, you’ll need a good magnifying glass, a guidebook, and a coin-searching tool.
There are two major classifications of RPMs: “S over Horizontal S” and “D over Horizontal D.” The former refers to a shifted mintmark. A shifted punch can cause a double image of the mintmark.
Most of the most popular RPMs of this date are Denver-issued. Although these are extremely rare, they can sell for a lot of money if they’re in mint condition.
While not as common, the 1938-S RPM is still pretty scarce. The mint mark is tripled, so if you find this type, you’ll be able to get a pretty premium price.
The 1960-D cent has over 100 re-punched mint mark varieties. This is a big reason why it’s so rare. And, while most of these are not in circulation, they’re still being discovered.
Another important point to keep in mind is that all mint marks were hand-punched into dies until 1990. That means that there is a chance that one or more of them were not properly heated during the manufacturing process, causing the die to fail.
Because of the high number of minted cents in this era, there are fewer RPMs available. However, new ones are being found daily.