My mother had a job coming up with such warnings. She was a 'home safety technician' for the local council, advising people not to fall off ladders and the like. It seems to work like there are statistics that so many people end up in hospital after falling of a ladder or whatever and the council thinks we must fix this, we'll hire someone to educate the public. The odd poster probably doesn't make much difference to the number of people falling but it was quite an easy and entertaining job for my mum.