First of all, it looks like the boy DOES like you, but just to be on the safe side, I'll give you some signs to look for to know if he likes you:
1. Keep an eye on how many times you catch her/him staring at you.
2. Take notice of whether he smiles at you a lot.
3. Look for whether he focuses on you in a crowd.
4. Observe if he has suddenly taken more interest in you.
5. Pay attention to any significant changes in his behavior toward you recently.
6. Start showing him a bit more interest and see how they respond.
One of the signs that a boy likes you is when he always teases you or makes fun/jokes.
Boys might not tell you directly, but they may tell someone. Or perhaps when you are not around but your friend is there he will ask for you.
Here are some of the signs: he acts distracted when he's around you and fumbles for things. From the corner of your eye you think he is looking at you but when you look up he turns away abruptly and you think you are imagining things. He tries to like all the things you do. Your instinct tells you that he feels for you but your rational part says you are sure to be wrong.
I think you can tell if a guy likes you if he always looks at you, he always wants to see you smile, he doesn't like it when other guys talk to you, he looks at you when you are doing something, he follows you places, he doesn't know how to act when he is with you.
He will make you feel special. He will be romantic. He will not move too fast. He will consider your feelings and take things slow.
He will show off, sometimes on small things.
If your crush likes you back him/her will subconsciously:
1. Play with their own hair
2. Blush when you are around
3. Straighten his/her clothes
4. Mimic you e.g. you lean forward and a few seconds later he/she leans forward
5. Cross their legs towards you
6. Show his/her palm
7. Change the volume of his/her voice to match yours
Examine his body language. If he likes you, you will see that his body position will lean forward toward you.
Keep close. Ever get the feeling that somebody is "in" your personal space - so much so that you want to step back? If he likes you, and you like him, neither of you will step back.
Notice his eye contact. If he likes you, he'll get it and hold it. Again, this can be uncomfortable if you don't like him or vice versa. You'll know if you feel like you have held eye contact just a fraction of a second longer than you would with anyone else, or if he looks away quickly.
Be aware of touching. He might put his hand on your arm when he laughs, or not move his leg if it happens to touch yours. This is a very good sign that he likes you.
Keep an eye out. His pupils will dilate (get bigger) if he likes you, but this is quite hard to pick up on, and you might look a bit weird looking that closely into his eyes.
Watch for him showing interest in things you like and do.
Joke freely. Does he laugh, even if you aren't funny?
Check for signs of nervousness: nervous laughter, sweaty palms, fidgeting, etc. Unless he's scared of public speaking and is about to make a presentation, it just might be that he's nervous about making an impression on someone he fancies (hopefully you).
Smile. A big smile in return probably means the feeling is mutual.
See if he always ends up in the same part of the room as you. Perhaps he keeps going out of his way to bump into you.
Pay attention to his friends. If they know he's interested in you, they might tease him subtly when you're around, hint to you that he likes you, or even try to find out if you like him. Also, study their reactions to your presence. Do they smile? Do they turn to him? If so, then there's a good chance he really does like you.
Those are all the signs I could think of, and I hope they helped you.