What are signs of a girl wanting to have sex with you?

Well in my experience, with 16-year-old girls, you know about it if they want to have sex with you. They're all over you and really flirty all the time. The only other option would be that she loves you and you've been together for a while and she wants to lose it to you. There are always exceptions, but that's how it tends to be.

As for the virginity pledge, it doesn't matter how anyone else feels about it, you really oughta stick to the people who agree with you. After all, it's your body.

So I'm guessing you have a girlfriend who you think wants to have sex with you but you're denying it her because you want to wait, right? Then explain it to her. That's all you can do. Explain that you always told yourself that you'd wait until marriage/you were in love/etc to have sex and you just don't want to do it right now. If she's worth it she'll stick around - just bear in mind that girls have hormones too, and either of you might get a bit carried away.