Please explain without contact. Physical?
Prolonged conversations. Veracious hunger to learn about
You. Weird awkward laughing or nervous giggles.
With contact? Ad eye contact or sudden down turns in gaze as you notice the may be looking at you. Nervousness in their demeanor, restless shifting etc.
Body language. Men and women express it differently but for me an easy tell-tale sign that there is chemistry could be in how closely a person may stand or sit beside you. Also check if your date or love interest is leaning forward to listen to you. Chances are someone who really likes you, enjoys being close to you and loves your company. :) If you get along with each other and are attracted to each other good things will happen I'm sure! :D
The signs could be only felt internally like a quickened pulse, sweating a bit, stuff like that.