Male flirting signals
Talking: Talking to a woman about oneself can open up a woman's mind to him. This is why in a relationship men speak during the initial stages after that, sticking to the facts, information and problem-solving.
Showing off the crotch: Men assume that displaying the crotch will attract attention, make the size known. It’s basically saying here I am, and this is what I am working with.
Looking dishevelled: Now this is interesting, men often don't even do it deliberately, but if they are to purposely put their tie off-centre or something that will require preening, they can get a girl to initiate touch with them and be able to test their interest.
Behaviour noticeably changes when you're around: Do they clam up, talk more, laugh more? How do they react to you in the room and orient themselves?
Moving into your line of sight: Does someone keep appearing in your line of vision? You might need to question whether or not this is deliberate. Often when we want to be seen as we move ourselves to ensure there is a chance of us being noticed again and again.
They are picking on you, joking about you or giving you backhanded compliments: These are all ways someone tests the waters before flirting more intensely.
They “view” or “like” all your social updates: With all the content flying around today if someone constantly is in your feed viewing or liking your stuff this may be an online gesture that they are noticing you and want to be noticed.
They point out their weakness, and your strength: This is a less mature way of flirting with someone, it's basically inflating their ego and playing the damsel in distress. Yet when a male does this its so enticing for women to run to their aid.
They always laugh at your jokes and come to back you up in conversation: Do they always laugh at your lame jokes? And when you're in a conversation will they usually jump to support your argument? These are all signs they are seeking your approval.
If you want to read up on more general flirting principles read Common Flirting Signals!
If a male is dropping any of these hints - he’s keen, or if you drop these hints they may help her to realise how interested you are.