It's pretty easy to tell if someone is interested in you. It's when you ask them on a date, and they say yes.

If they say no, the respectful thing is to drop it.

Do the respectful thing. This is really uncomplicated. There aren't any "ifs" or "buts" after that. The notion that this is the time to start wooing is absurdly wrong. That's the time to know you've been rejected, and move on.

Accepting rejection, incidentally, seems like something many of these VCs have trained themselves to be terrible at professionally.