I don't think there are many men who can tell straight away, especially ones who are not very upfront and confident and even then a lot of the confident ones will "have a go" with out really knowing. <br />
The easiest way is for a woman to tell him and pay him compliments. There is a lot to be said for polishing a man's ego...even if he doesn't know she likes him he's more likely to say something after he's had a bit of a boost
He sends out a signal and sees if she responds to it.
Look.i have been a male .straight.for 37 years and i will tell you that men are stupid on all things and NO they dont know you like them.
No women don't show it in anyway. Hence the "how can I get him to notice me" thing. To which the answer is "He's already noticed you and you've behaving like all the other women; i.e showing no signs of interest".
Usually women are a lot better at telling than guys..