Generally according to the law on jewelry marks, the maker must put that mark near the quality mark. The quality mark is the one showing the metal used.
925 is a standard stamp for sterling silver. Other marks include the word Sterling and abbreviations of that. The 925 show how much silver is in the metal, or 92 1/2% silver (with the rest being copper). That is the recognized and legal meaning of sterling jewelry metal.
I say the ring is sterling make by some manufacturer with a hallmark of RSC.