Commitment to say yes. Assuming you mean copulation. One night stands are no longer in my repertoire. As a born again virgin, I would have to say that no sex before monogamy. I would have to have a mutual discussion on many parameters prior to any hanky panky. Presumably that would occur over months of courtship. Perhaps one day after rigorous vetting I might acquiesce & permit him to hold my hand. But then being of a certain age I have no need for frivolity. I am partial to substance & integrity. Others may hold different credentials.

He is coming on to me if he gets too close. Holds eye contact too long. And don't touch me.
Coming on to you? Flips her hair. Eye contact for a too long duration. Giggles. Turns toward you. Smiles then looks away. Bends over and shakes her ass. Jumps on you & begins the horizontal mambo.

For me after reading several books on body language I would have to say if the woman is responsive to my conversation, usually and on occasion I would touch her on the hand or on the side of her face, just see her reaction.
Now this is all from initial contact but can get a general idea how she is thinking.

I believe it depends on the person, in general, there are changes in body language, attention may increase, changes in face expression, particularly in the eyes, the tone of voice may vary, there may be an increase in physical contact and the use of language may change and become more playful.

Mmmmmm For me. . And for whatever reason I feel a vibe. . Or depending where we are a comment or a play on words or a touch. Then there is the look in the eyes

Very philosophical you say.