1. He makes statements about you. He’ll say “you’re the kind of person who” or “you’re always doing x”. He’s learned information about you and cares enough about it to communicate it back to you. You’re on his mind.
2. People bite their lip or cover their mouth when they are subconsciously trying to hold information back. If a guy is doing this, he might be trying to watch his mouth to keep from saying something that either makes him seem unappealing, or lets on that he’s interested in you.
3. They smile a little bit when you make eye contact with them from across the room. And they smile a lot when you first see them and are saying ‘hi’ — especially if it’s accompanied by a hug.
4. He makes excuses to touch you.
5. At a party, they follow you around. If you’re in the kitchen, they’re in the kitchen. If you’re playing Guitar Hero, they’ll be in the room with you. If you’re outside getting some fresh air, they’ll follow you.