What is a common signal for vehicles to indicate they are backing up?

Sounding the horn briefly prior to reversing is a commonly accepted signal for vehicles to indicate they are backing up. This practice serves as an auditory warning to alert other drivers, pedestrians, and nearby personnel that the vehicle is about to move in reverse. Utilizing the horn is vital for safety, as it helps ensure that others in the vicinity are aware of the vehicle's intentions and can take appropriate measures, such as giving way or stepping back.

The other options may not be as effective or standardized in communicating the vehicle's reversal. For instance, while flashing hazard lights might indicate a vehicle is stationary or experiencing difficulties, it is not specifically recognized as a signal for reversing. Waving hands out of the window is an ambiguous gesture that may not be immediately understood by onlookers, and turning on the rear lights, while helpful, does not serve as a clear indication of the vehicle's intention to reverse without additional auditory warning.