He Becomes Very Appearance Conscious
It's natural for everyone to want to look their best around someone to whom they are attracted, and men are not an exception.
Check for telltale signs in his appearance that he's going out of his way to impress you. If his hair always seems carefully styled or his outfit is always more carefully put together than usual every time he knows he will run into you, it's fair to speculate on his motivation. Additional clues include smoothing out his hair or straightening his tie.
He Gets Fidgety
It's not uncommon for a man to become a little nervous around a girl to whom he's attracted.
Observe his speech and body language for details. If he seems a little jumpier around you than he does with others, it may indicate a romantic interest in you. If he's typically smooth and mild mannered in speech and becomes tongue-tied every time you talk to him, the evidence becomes even stronger. Also watch for excessive clumsiness in a guy who normally does not fit the part.
He Picks Up Your Interests
If a man is attracted to you, he will try anything to get closer to you and spend more time with you.
If he suddenly develops a passion for a hobby he knows you are into, his interests may actually center on you rather than the hobby. The more he has in common with you, the better chance he may think he has of getting you to like him.
He Makes Efforts To Catch Your Eye
A guy who is attracted to you will want you to notice him.
If he's standing in a group of friends when he knows you are nearby, for example, he may alter his position to ensure you see him clearly within the crowd, separating himself from his friends in the process. He may try any number of attention-getting strategies, whether they involve a subtle movement or an obvious attempt to amuse you.