What are signs someone has a crush on you?

Me, I think I'm the only one in my group of friends no one crushes on. A couple of my friends who are guys, they get attention from ladies, and well, most of my friends are girls and I hear what they talk about, including boys, and who's hot and all that stuff. Me, well I never hear my name ever. I even ask if anyone has a crush on me, I always get "no", or "not that I know of". Either a no or an indefinite answer. I can't help but feel bad because well, other guys get crushed on, but me, when it comes to girls, I'm just a shoulder to cry on, that's how I see things. So, I don't believe some of these female friends, because I'm sure someone out there likes me, right? What are signs someone likes you? What are some more obvious signs? What about less obvious ones I should look out for? Any ideas???