Single women: do you ever wear a ring on your left ring finger?

I’ve noticed that some of my unmarried female friends have started wearing rings on their “wedding ring” finger,even though they are not married or engaged. Is this common? One of the 1st things I check out when I meet an attractive woman (ok, the 3rd or 4th) is her left ring finger to see if she is available. Now I wonder if I’ve missed my chance with several interesting women because I mistakenly assumed they were married or engaged just because they were wearing a ring on that finger.