As a single gay man living in San Francisco, I would have to disagree with the recommendations to go with the right hand.
If I see a band on the left ring finger of a cute guy, I know he is spoken for; if I see a band on the right ring finger I don't really know if he's in a relationship or just accessorizing. I think the need to 'differentiate' from hets on this is misplaced; unavailable is unavailable. I'm very non-assimilationist, too, so my stance on this is not biased by any desire to 'fit in'.
Oh, & the 'right earring' thing was not really about gay vs. straight, but about um... something Eric's grandmother wouldn't care to know.
Edited to add last paragraph.