My question is, what led to the law prohibiting harassment?

In my opinion, signs like that are meant for Darwin Award Winners. They are a kin to the sign on a bridge that says "No jumping from bridge".

When we visited Everglades NP we witness some foolish chick grabbed an alligators tail and dragged it a foot or so. She was clowning around for her friends. There were tons just on the banks sunny themselves. I was so hoping she would get bit.