A lot of warning signs show up after someone makes a mistake. It’s to stop people from doing ridiculous shit, like drinking water from a urinal, getting sick because of it, and then suing because there was no sign saying they shouldn’t drink from the urinal. In this case someone put it up for giggles.
Well what’s the point of having a drain in the restroom floor if you’re not allowed to use it? The urinal has splash back and people use their dirty hands on the handles. Besides, it’s much more efficient to just drop trau and let loose. No need to walk all the way to the wall or even wash my hands.