This vital piece of jewelry is the proof of Marcy too having "strayed" in Season 2's "Girls Just Want to Have Fun" two-parter. The episodes revolve around both of the Rhoades treating the opposite sex like pieces of meat, but when Marcy meets "Zorro" at Troy's strip club, she completely loses her head, and her ring down his pants.
Presumably, this is not the same ring she wears when married to Jefferson D'Arcy from Season 5 onwards.