This thread got me wondering about the above question. I have a hard time IDing gay men unless they are “flaming”, but gay women seem to be easier. My theory is that they sometimes acquire a habit of not looking at or smiling at men, in order to avoid unwanted attention.
Before I get slammed for stereotyping, I want to add that this is definitely not true of many of my gay women friends (of whom I seem to have an inordinate number - what’s the male equvalent of a “fag hag” - a “dyke tyke”?), but it seems to be true for a significant proportion.