This is a Serious playground where there is no playing allowed in the park.
Obviously the sign has been tampered with, as the other two words are center justified. I’m guessing this missing word is horse, but perhaps it’s funny if you think of other words to put in there. Banana, Dog, Jet Ski or whatever you can think of, it’s now a sign Mad Lib for your amusement.
Also, I’m very disappointed in the internet today, because there was very little that I found that was somewhat funny. Aside from this funny hacked photo there is this martial arts prank video.