I hit a car and there was no damage done, but the driver didn't signal for us to stop?

It was as I were were slowing at a red light. After a few minutes without my immediate notice, my foot started to release pressure on the brakes, making the car move forward slightly. It very lightly bumped the car in front of me, a silver honda civic. At that moment, the light turned green. It was a silver car, like I said, and I didn't see any damage whatsoever. The woman in the car who I hit looked at me through her mirrors. I started to see her hand go up in her car, with a rectangle looking object, her phone. She never held it out of her car, but kept it inside and sped up and raised it to take a picture, I'm guessing. We kept driving and she never gave a signal for us to pull over. My car is grayish-blue and I didn't see any marks/scratches. All I saw was on the left, slightly high left of the bumper on her car was this grayish/darkish blotch, an oval shape that wasn't in scratch form. I don't personally think this was of my damage, maybe it had already been there. I eventually turned to move into the right lane (the furthest one to the shoulder). She moved over as well but didn't signal anything. We later stopped at another light and I pulled down my window and started waving at her. She had her window down as well (I saw from her mirror) and tried to shout "Miss! Hello!" and wave. I don't know if she saw me or not. After the light she kept driving and went back to the middle lane and I tried to follow her but cars interrupted me. I don't know what's going on.

Fuggedaboutit! First of all, she was ahead of you. So if she took off it means she either was unaware of it or thought it was of no consequence. This has happened to me several times, both my fault and fault of the other driver.
There's always a concern about a double cross, but since she took off and you made extraordinary (in my opinion riddiculous) efforts to acknowwledge the accident, I don't think you have anything to worry about.