In my experience, the “NO” figure should be bent over a bit more in order to project onto the wall behind the toilet as well as the ceiling above. No better memory of working retail than going up to my boss and explaining why I needed to know where the spare ceiling tiles were.
Reminder to anyone still working retail: if your job description isn’t “janitor”, you don’t need to clean that up. It’s a biohazard and they can pay more expensive people with better equipment to do it.
Are you aware of the legendary Ryan's Steakhouse story?
Hell, that thing might be an urban legend, but it's supremely well written and if I was in graphic design, that story alone would probably lead me to thinking that selling signs like this would be a good idea.
If you haven't heard it, a web search for "The Steakhouse incident" (with quotes) or "macaroni beef toilet story" (no quotes) will probably turn up yet another re-hosting of it.
Having seen the occasional superfunded chain restaurant men’s room, I know for a fact this sign is needed, and yet probably won’t help. I have to imagine the kind of person who will do that to a restroom, and leave it that way, isn’t going to see this sign and say “OOOOOH that makes sense. I was totally gonna do that until I saw this sign.”
Having worked as a dishwasher in a chain restaurant, whose job it was to clean the bathrooms in the middle of the day after a busload of septuagenarians have done pretty much this: Yes, yes we absolutely need this sign.
In some countries the toilets are sort of embedded in the floor and you squat over them. There’s some evidence that this is a healthier way to poop. But if you’ve only ever squatted in your life a toilet might be as confusing as the three shells.