I was walking in the same direction as a girl at school and she turned her head really fast and looked at me, so it seems she wanted to know if I was looking at her butt. She must've wanted to catch me looking or she wouldn't have looked so fast. She said "hi" to me when she walked passed me saw me, so she knew I was there.
I've seen that a few times and I'm not sure if I should take it as a compliment or what. Does that suggest there's some interest and the girl is kinda hoping to catch him looking? They just want to catch the guy red handed or want an ego boost?
Depends on the girl. More insecure girls will do that in hopes that he isn't and if he is, he likes what he sees. More confident girls will do it to catch him and maybe tease him a bit in a flirty way, IF he's cute. Other girls may just look to see if you are following her. I do that sometimes when I'm in areas that are sketchy or unknown to me. You can take it as a compliment if she doesn't say anything about it and just keeps going. That means she doesn't mind you looking at all.