What do mandatory airport signs indicate?

Mandatory airport signs are critical for ensuring the safety and efficiency of airport operations. They provide vital information regarding where aircraft may not proceed, highlighting entry points to runways, critical areas, or zones that are off-limits. This type of sign usually features a red background with white lettering, making it easily recognizable to pilots and ground personnel alike.

Understanding the importance of these signs is crucial for maintaining operational protocols at airports. They help prevent incursions into restricted areas, thereby reducing the risk of accidents and improving overall safety on the airfield. The other choices focus on services, emergency exits, and maintenance schedules, which, while important, do not specifically pertain to the mandatory signaling required to direct aircraft movement on the ground.