What are the immediate signs a girl will give to show attraction or non-attraction?

She'll go out of her way to be closer to you, in any way she can. Hitting, kicking, sitting near you, etc. All good signs. If she thinks you're gross, she'll try to avoid you. She'll smile at you a lot, make eye contact, and laugh at all your jokes. Come to your defense if someone insults you. You'll know.