MM on this 51S looks like the RPM001. Also looks like there is a die clash on the obverse going into the forehead of Jefferson. Reverse is machine damaged. http://www.varietyvista.com/05 JN RPMs/1951SRPM001.htm Pulled it out of bank wrapped box today.
I don't see anything on the reverse that would correspond to the mark on Jeff's forehead. Maybe it is a die gouge. Chris