Just because they don't say it, or point it out, does not mean they don't know or don't suspect. They might be very supportive of ->-bleeped-<-, they might just be being politically correct, they might not care enough to question it, they might be big city people who know better then to confront someone they consider off the deep end. You can know peoples' behavior, but rarely, if ever, their intentions.
And yeah, people in a LGBT club are more exposed to it. I know a lot of LGBT bars where they would know right off, because the non-trans women who come in there don't look that good, or pretty - ever. I've been told by quite a few people that the hardest place to pass is San Francisco where 'spot the ->-bleeped-<-' is almost as much a sport as 'guess why the other people on the bus aren't allowed to drive cars.' Again, its a matter of familiarity.
I mean I don't speak or read Japanese, Chinese, (Mandarin or Cantonese), Koren or Vietnamese - but by being around that most of my life, I can look at a sign and tell what it is, even in its English translation. To someone who was raised in say Kansas and never seen any of that I'm pretty sure it all looks the same. I'm even more sure that they would have an even harder problem guessing who is who, but again, familiarity brings you to the point of noticing those very fine details and differences, so you can tell if someone is Japanese or Chinese. Someone like Barbie who was born and raised in Korea can probably tell from two blocks away.
Consider that despite all the 'do I pass' photos and questions about haircuts and all - most people can correctly guess gender from the back, a half a city block away just by the basic dimensions of the body.