What must be displayed if a load protrudes more than 4 feet beyond the rear of a vehicle?

When a load protrudes more than 4 feet beyond the rear of a vehicle, it is essential to display a red flag. This requirement is in place to alert other drivers to the potential hazard posed by the extended load, ensuring that they can maintain a safe distance and avoid collisions. The use of a bright red flag provides high visibility, especially against various backgrounds, making it easier for motorists to recognize the oversized load.

In the context of load safety regulations, other options such as a warning light or a safety cone are not standard requirements for indicating an extended load. Furthermore, not indicating the load could lead to dangerous situations on the road, which is why a red flag is mandated for such cases.