What is the hand signal for 'Stop'?

The hand signal for 'Stop' is indeed represented by swinging the arm at a right angle to the track. This signal is universally recognized in various fields, especially in railroads and construction, as it indicates an immediate cessation of movement or action. The distinct positioning of the arm at a right angle ensures that the signal is clearly visible and understood by all personnel, even from a distance, thus enhancing safety and preventing accidents.

Additionally, this method's effectiveness lies in the simplicity and clarity of the motion. It minimizes confusion and ensures that the recipient of the signal can quickly assess the need to halt their activity, which is crucial in scenarios that require rapid response. This clear delineation helps maintain operational safety and coordination among workers.

Other options, while possible movements, do not convey the immediate and unambiguous message of stopping, which is critical in ensuring safety across various engineering and operational contexts.