I don't have any. And when I do get a crush, I move on quickly because there is no use dawdling over an impossibility. If I think they're attractive, then I might get a sort of mini-crush on them. When I say attractive though, I don't just mean looks-wise, because personality factors into a lot too. I won't crush on someone no matter how attractive they are if they don't have a good personality, and vice versa. I won't crush on someone no matter how good a person they are, if they aren't at least a little attractive to me. Crushes are pretty much just that, crushes. I'm totally done being crushed.
I would say that I have a few number of people crushing after me, not to sound conceited or anything... . I can usually tell when someone is crushing on me. There is obvious signs, like what their eyes do, their body language, voice pitch/tone, their attitude towards me/other people, to name a few. When people crush on me... I tend to tell them(if the cat gets out of the bag or whatever) whether I feel the same way or not :s. I don't like being a heart breaker :|.