What does RSG on a gold ring mean?

On any piece of fine & semi-precious Jewlery RSG- denotes a Pre-assembled piece of Jewlery that does not have certification on gems or components. (These pieces can generally not be "Traded Up" given the lack of certification.) RSG- literal translation is "Ready-Set-Go": Meaning a preassembled piece that is ready to be set w/ stones, and sold. Often found in items advertised in chain stores as a "special" earrings, bracelets, pendants. It is uncommon, to find RSG on a single piece w/o components or gem stones.
RSG, are a mass produced setting, then set after production. Hope that helps!