Do you think it is an RPM though......how could it not be with a bar clearly visible and very bold inside of the "D"?
Looks more like a deteriorated die/worn strike to me. Look at the flow lines coming off the building.
If I can get a good picture of this RPM you will like it just to be able to see a RPM like this don't happen every day I didn't mean to use some one else thread but I was looking at different types and I seen this one I'm going to take a picture. Give me a minute see if I can get a good picture don't want to take all day trying to do this here is the real deal one off a kind I collect old jefferson nickels so I know when I see something.