Well if paddyman98 says dirt I'm going with him, he spends enough time digging in it so he would no. Lol Dave
I can't see anything, but it's hard to tell from the picture. Since you have the coin in hand, check the following sites. They have listings for known RPM and OMM http://www.varietyvista.com/ http://doubleddie.com/58243.html
I don't know it's all dirt. The area below and to the left of the MM doesn't look like dirt to me. The part that's dirty is inside the D.
Sometimes is hard to tell by the pictures. Check your coin some more here. http://www.lincolncentresource.com/OMMS/OMMS.html
When checking your MM for a variety such as an RPM, it is best to start with the MM placement. Especially in the case of identifying a worn/or damaged coin.
I do not believe it is an RPM. Just wear that has flattened it a little. The same font is used for the "D" and corresponding "S" for the same year, except for Large S-small s, etc. You can't get part of a RPM in the middle, but not , on the same coin, someplace on the out side of the main mm.
