What are the laws/rules regarding "busking" or subway entertaining in NYC?

are there rules? do you need a license? can anyone just stop and set up a little spot to make some extra cash? I’ve seen people who undoubtedly have NO talent, yet they show up with a violin and make horrific noises and have a bucket for donations. can anyone do this, or am I going to be the moron who starts doing something and gets kicked out and humiliated in front of everyone?