What Does It Mean?

Evil

Serious question: if a girl is wearing a ring on her ring finger (left hand), does it 100% mean she's engaged or married? Are there any occasions where someone would wear a ring on that hand for any other reason?

I ask because there is this super cute (hot) girl. Recently I've noticed that she has a ring on her ring finger. I dont think it was there a few months ago. Anyway, it looks nothing like an engagement ring. It looks more like a class ring. The band is sort of yellowish / antique-ish in color. And there's a stone on the ring, but it's small and I think it's also black (or dark). It doesnt look like the typical engagement ring... and I've seen dozens of chicks who couldn't hold a candle to this girl strut around in ginormous diamonds. Evil is confused. Can someone help clarify?