It has the appearance of one, a 4" square butt model 10, usually stamped RHKP on the backstrap along with a rack or inventory number. Some were also stamped C & E, for Customs & Excise, and a number.
I agree, it has the round lanyard ring the RHKP's have. I am posting a pic of the backstrap stamping found on them, dont have a C&E to show you but I am working on it!
Here is mine. Maybe someone will enlighten us with the serial range of the RHKP and C&E mdl10's. I have never seen a reference to serial ranges and differences in the two stampings and would love to learn.