How to give good signals to a girl ?

It works in movies. Not in real life. At least from experience mine and mine friends. If you like her try to spend more time with her. If she will be eager then she likes you. If she will make excuses she doesn't. Of course it can change overtime but I don't know how long you know her.

It depends a lot from character of her. I know one girl that if you would not tell her this in open text would never get it. But once she got it from my friend she was really happy.