The origins of this phrase goes back to a middle signal light called the “OK light” on trucks. When you wanted to overtake a truck, you were supposed to tap yo

The origins of this phrase goes back to a middle signal light called the “OK light” on trucks. When you wanted to overtake a truck, you were supposed to tap your horn, and the truck driver would flash this middle light to tell you it was safe to overtake. That signal light disappeared decades ago, but that phrase remains. It was originally: “Horn Please” above, and “Ok” written under that signal light.