Final answer:
Any load extending 1.5 meters or more from the rear of a vehicle must be marked with a red flag or sign to alert other road users.
Step-by-step explanation:
The question pertains to road safety regulations, specifically how to properly mark loads that protrude from a vehicle. In many regions, the correct way to mark any load that projects from the rear of a vehicle by 1.5 meters (5 feet) or more is with a red flag or sign during the day, and typically with appropriate lighting or reflective devices at night. This is to ensure that other road users can clearly see the extended load, preventing accidents or collisions. When transporting a load like this, ensure it's securely fastened and marked to avoid road hazards.