Drool. A head nod. A wink that looks like one half of his face just suffered a sudden muscle spasm. Pancakes of sweat under his arms. Boners. When a guy is attracted to you, he might stare. This stare can look like many things. He might stare at you the way a hungry dog might stare at a bowl of chicken wings placed beyond his reach. Or he might stare at you like some sort of alien probe, using his ocular sensors to unravel your DNA. He might also stare at you with crazy, glowing finger eyes. But he will most likely stare.
If the guy is partially self-aware or marginally socialized, he might come up to you and engage you in scintillating conversation. He might say “Sup?” He might say “So…” He could even say “You ever seen that wild YouTube clip with that dude who tried to eat a live eel and he almost did but then he puked the eel up, it was totally sick. Have you seen it? Do you want me to pump this keg for you? Are you on Facebook? I like peanut butter and Ritz crackers? Yes! I do! Do you? Hi.”
I think knowing whether someone is attracted to you isn’t really gender specific. It’s sort of like gravity. Gravity is invisible, but it’s there. Which I found out last weekend when I rented a bike. There is a charge in the air when two people find the other attractive. This happens before any subtle signs. But if you need a sign, then ask yourself if YOU’RE attracted to him. If so, smile. Make eye contact. Talk about the pretzels on the bar. If he talks to you, then he’s interested.