There are methods of telling if somebody is gay, for instance social media, voice( not always, may just be affeminated but who knows), movements, or interests. Usually alot of people post it or announce it, talk about it, but there's also alot of individuals who'd rather keep it private or so. Either way, I'm gonna have to go with grindr to.

Though in all honesty, I'd say that a gay guy would know what to look for when trying to gauge another person's homosexuality.  Just like straight guys would know if a girl is interested in a guy and vise-versa; gay guys would recognize the subtle things of what a gay person is interested.

Also, with modern day technology displacing the cruising scene it is much harder to identify gay people. The art of the cruise is disappearing. In the 70s and 80s you could walk by another gay person and just the way you would look at each other; like the lingering stare, how long you held eye contact, whether there was a secondary, a double-take would be enough to tell you that person was gay.  I,f that wasn't a tell tale sign, they had other ways of communicating their gayness using semiotic language , or the language of symbols, with things like the hanky code, which a lot of this new generation haven't heard of.  The hanky code was basically a sign system using multiple color of handkerchiefs. The different represented different scenes.

For instance, if you were a gay man that was into fisting you would wear a red hanky, and depending on what side you wore the hanky on would tell the person that was looking to cruise you whether you were a top or a bottom or verse.They have hankies for water sports, scat, or drug use. Virtually any scene. You name it they had it. Also, is fairly easy to tell in the 70s that a gay person was gay by where they spent their free time.  If you were a New Yorker, people were down by the meat lockers. In Chicago it was the Belmont Rocks. In my town it was the State Park. A lot of tradition and symbol that have gone by the wayside because of modern technology. Instead of going to cruise somewhere, and try to meet somebody organically, you just pick up your smart phone and order out for dick on Grindr or Scruff.

As for lesbians, I have no idea how they meet. I think they hang out at Home Depot.