What does the yellow and black strap across the door opening signify?

The yellow and black strap across the door opening serves as a safety precaution when a loading bridge is absent. This marking indicates to ground crew and personnel that the door should not be accessed without caution, helping to prevent accidents or injuries during the boarding or deplaning process. This visual cue alerts individuals to be aware of the potential for a direct drop or gap where the door leads to the outside of the aircraft.

While other options mention the status of the door or are related to standard operating procedures, they do not specifically address the purpose of the strap when there is no loading bridge. The strap's design and coloring are intentionally chosen for high visibility, making it clear to anyone around the aircraft that special attention is required in this area.