It looks as a re-punched mint mark. If it was mechanical doubling, then other areas would have been affected as well. All mint marks, were added by hand stencils then. They were later added to the master dies later. It's not listed in the Cherrypicker's guide either
"Note that the R in LIBERTY should be a different font than the R in TRUST, with this coin they are the same font." posted by statequarterguy I compared the fonts from 1983s on ebay and the one posted here. They look pretty close to me. Read more: http://www.cointalk.com/t213204-2/#ixzz25pynN7Vl
I’ll admit, it is difficult to see and it is a minor difference. Note that the right leg of the R in LIBERTY for the ebay coin (and all others I’ve seen) appears to have a straighter slope than the R in TRUST. For the R in TRUST for the ebay coin, the posted coin, and the R in LIBERTY for the posted coin, the slope of the right leg of the R is less, more like 90 degrees. Later date Lincolns have similar R’s in both TRUST & LIBERTY, but not in the 1930’s. Because of this slope difference, the R in LIBERTY on a genuine 31-s appears more narrow than the R in TRUST. In the side by sides you posted I can see other difference as well. Another way to see the R difference is look at the field in the space between the legs of the R in LIBERTY. Note how much more narrow the space is on the ebay coin and all other certified 31-s I’ve seen. If it is a fake, I’d say rather than wear on the hair, it’s intentional buffing to cover up hair details that are almost never correct on counterfeits. You know, as was mentioned, the discovery of an unknown RPM for a coin whose entire mintage has been saved and examined probably millions of times, is a dead giveaway that this coin is 99.9999% a fake. Based on that, I looked at the minute details that matter for counterfeit detection. More than likely the counterfeiter was inexperienced at sinking mint marks and blew it like a newbe at the mint. But then, I could be wrong. I’d say get it certified if you think there’s any chance it’s real.
Sometimes people don't consider ( or at least underestimate ) the engraving skills of people before the advent of Computer controlled mills and such. At least eliminate the possibility of an added mintmark on a 1931 P cent. This could be done by carefully removing one from another year cent ( maybe why it is shaped differently) and gluing or silver-soldering it in place. Many "youngsters" might think that impossible, but it has been done many times in the past. A second way was to drill a tiny hole in the edge of the coin nearest where the mint mark would be , and then insert a small gravure and raise the copper in the shape of the mintmark ( difficult) , but also achieved. A 3rd way was to drill a larger hole and use a small tool with a mint mark shaped end and insert it and tap until the mm shaped end pushed a mintmark up. Any of these could explain the condition or shape of the mint mark. But they are eliminated if the edge shows no filling of the hole and the mint mark is not glued or soldered. That takes a higher magnification and observation of the edge , more than the photos given show. Probably best to send for authentication. Jim
Send It to CONECA. You never know...I sent in a 1945 Mercury dime and even after 66 years,no one ever found one like it before.......its a discovery piece (DDO #5)