Ruger Security Six backward RP stamp ???

[BGS_Tactical]

Just picked up a Security Six and the barrel has a stamp on it. It is a backwards R followed by a P, in a circle. The R and the P share the same leg. I dont have this on any of my GPs, was just wondering if they are all stamped or what this stamp means.
Thanks,
Brad

[Highspeedlane]

I believe what you're referring to is an "S" superimposed with an "R", which represent the founders Sturm and Ruger.