@spendius,
I saw a truck reversing into some school gates. Open ones, obviously. It came twice a week to shift the trash the school produced. Not the kids of course.
It had a warning device when in reverse which went "Danger. Vehicle Reversing." It was in a "speak your weight" machine style of voice only louder and more grating the nearer it got to where the large metal bins were stationed, just outside the rear service door, in a sturdy cage which only the Senior Dinner Lady, and Her deputy, had the key for.
30 or 40 times it went "Danger. Vehicle Reversing." as long as there were no hold ups presumed short enough for the driver to think of taking the damn thing out of reverse.
Cheap plastic bins without protection had proved inefficient.
I knew a chap who had a car horn which played a short tune. Beepibeepibeepi like but in English it meant "Do you come here often?"