Was true a long time ago, when gay people had a much harder time being openly out and as such made use of little tells to communicate with other people in the know.

Might be true to some extent today, for someone who for one reason or another wants to make homage to the symbol. But while someone with an earring in just their right ear is more likely than average to be gay (most people preferring either a matched pair or none), most gay people I've met don't give a toss about archaic codes. Or, for the most part, earrings.