Please Do Not Assault the Staff

In any British post office, doctor's office, train station, or bank, you are likely to see a sign bearing some variant of the message "Do not assault our staff. It's not nice. We will call the police."

I'm not sure what (if anything) this indicates about the British character. That such assaults are so common that the signs are necessary? Or that the sign-posters have such faith in the human nature that they think the signs will do any good?