the best ways to tell someone is attracted:-
Raises there chin so you can see more of there throat
Eyes dialate.
Stares at you(Including mutual staring).
Blinks at a similar rate to you.
Draws shoulders back, may include hands on hips in pockets etc.
tries to make you smile/smiles when you do.
Bites there lower lip.
If they feel intimadated, drawing feet closer together. (Including shy)
Mimicing your reactions.
Quick to react to when you are speaking to them.

These seem to work whether male or female. (Straight or Gay Attraction)

If someone is shy when they are around you this is a good sign :)

Good Luck