Are wedding bands a good clue to if a man is single?

I have to admit that when I meet men for the first time, out of habit  I check their ring finger. If they are not wearing mens wedding rings, I think they may be available. I know that is not always the case, but my question is, why would men not wear wedding rings now? I know a long time ago, it was less common, but I would think the married would show off their rings. It just makes it harder for us single girls out there to know what is what.