If someone have a crush on you, there are a lot of things through which you can identify but on the other hand there are many things through which you can not even judge that the other person have a crush on you..
I am listing down a few through which you can identify:
1. The person keeps looking at you directly, until and unless you notice. And once you notice that he/she is looking at you, they start to ignore.
2. The way the person treats you (in case you know each other since long) if that have changed from the behavior in past then definitely he/she have grown feelings for you.