I look like SoccerMom. In fact, for a long time, I was one

. And while being gay certainly isn't all I am, it's an obviously big part. I also don't introduce myself with "Hi, I'm gay!" So I get it.
The only time anyone is sure, is at Reunion or Pride (but many straight people go to Pride, so that's not even a good example).
If you are in college, there's probably a GLBQ club on campus and you can find community there. Some find the courage to wear a rainbow something on their clothing, but that's not even a foolproof method. It's hard!
You made a good start by coming here

.