What are the signs that a girl has a crush on you?

it started 2 weeks ago, i noticed this girl looking at me (even until now) i think the number of times me and my friends caught her looking directly at me is 17 times within a day, that seems to be the record so far, i thought it was just her prank but then the way she looks is like she's serious and often times she's smiling sweetly. well, this is what really bothers me, every time i p by her she seems very snobbish to me but then she will always have a second look right after we p by each other. guys, i really need your help. thanks.