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 

.