I don't see those signage on cars in the USA, but there are a few places where cars are explicitly told to blow their horn, example: https://goo.gl/maps/WWC4ACV

I don't see those signage on cars in the USA, but there are a few places where cars are explicitly told to blow their horn, example: https://goo.gl/maps/WWC4ACVRdeyUQnZ57 https://goo.gl/maps/WWC4ACVRdeyUQnZ57