From a changing room:
This sign has a multitude of problems:
Number one is "It exists, and therefore damns the entire male gender."
Number two is "The targets exist, despite the wide availability of bludgeoning instruments."
The third is "assuming the target can read", which is like a sexy co-ed hoping that the axe murderer is distracted by the fine lacework on her skimpy nightie. Any information campaign has to intelligently target their audience, and "writing" might be a bit highbrow for someone prepared to walk into a public place and fire their face into the facilities like a snot-loaded shotgun.
Perhaps marking the area with urine or a dismembered carcass might be better suited, and still less disgusting than naked men blasting streamers of mucus, like the worlds worst party-popper, all over the place people wash their hands. Or at least did until they saw this sign.
"Refrain" is a problem too. Some snotgunners might actually read the sign, because even Neanderthal man made marks on the walls of his cave, but "refrain" will jam both their neurons until someone finds an English-to-grunt dictionary. When scientists taught gorillas sign language they used words like "hello" and "pretty", rather than "Felicitations" and "delightful". I wouldn't want to make insulting comparisons, but gorillas have never come into my sports center and blown their noses into the goddamn sink.