My car's "belt's" light came on today, what could that mean?

I drive a 1996 Mazda Protege LX. Sometimes the engine belts squeal like a pissed off piggy when I turn it on, the a/c compressor is a dud but basically it’s fine. Today halfway through my two mile drive to work the red ‘BELTS’ light came on with the little picture of a passenger, sometimes it goes away particularly when I shift my safety belt. I tugged on the belt to make sure it still locks up when pulled, it does. Other than the light I have noticed no significant changes. Any ideas on what it is? How much I should pay to get it checked or how much to get it fixed? Is it very dangerous? I’m a complete damsel in distress when it comes to things that go vroom.

(I know the a/c and engine belts probably have nothing to do with it, just trying to be thorough.)