Signs in Florida

I've been always fascinated by the signs that people put on streets and roads in order to explain to the random strangers how they expect them to behave in their town. Being an almost professional stranger I have a whole collection of the signs from different countries. Here are some new ones from Florida.

This sign got me baffled. I've never seen anything like it. Does it mean the maximum swinging speed of a seesaw?

And yes, they do have championships in underwater hockey!!!! Can somebody tell my the rules of this game?