What indicates that all traffic must stop regardless of direction?

The correct option, which involves one arm raised vertically, indicates that all traffic must stop regardless of direction. This signal is universally recognized as a stop signal, and it is commonly used by traffic controllers or officers to ensure safety at intersections, roadblocks, or during emergencies.

When a traffic manager or officer raises one arm vertically, it creates a clear and unmistakable command to all vehicles and pedestrians in the vicinity to come to a complete stop. This gesture emphasizes the need for immediate compliance, preventing accidents and ensuring smooth traffic flow in potentially chaotic situations.

In contrast, the other signals do not convey the same clear message. For example, a single arm waving might suggest to slow down or proceed cautiously, but does not provide the definitive order to stop. Similarly, two arms oscillating may suggest directing traffic or indicating specific movements for drivers, rather than a complete halt. A leg raised on the road is not a standard traffic signal and might confuse drivers rather than provide a clear instruction.