I was at a pawn shop this morning looking to see what might turn up. There was a pre-war K frame .38 with the subject marking underneath the usual .38 S&W Special marking on the left side of the barrel. I'm not very savy about older Smiths, but I had never noticed this mark before on a S&W. It seemed unusual to me that the .38 special would be refered to as the "U.S. Service cartridge". Is this a common marking? Just curious.