BEWARE OF FALLING SUBJECTS
In London, they urge you to look to the right before crossing the street and to mind the gap (between the train and the platform). In Germany they love bans, especially strict ones.
In Communist Bulgaria public signs amalgamated the idea of urging people to do things deemed safe for them and to ban them from other things that are dangerous or unhealthy. To put it in another way, they taught people how to live and behave.