OP;
From the photo your frame appears to be nickel. If so then the other side of the frame should have a factory stamped letter "N". If yours was originally blued finish, then there should be no N stamp, and the R may indeed be a 'refinish", but as others have said it may just be a casting inspection code.
If I am just seeing the camera flash and not nickel then disregard the above.
A Letter would tell you some information at least the original factory configuration and finish and the ship date to original dealer/buyer/store, etc.