How should an employee signal to stop a train?

When signaling to stop a train, the correct method involves moving an object to and fro across the track. This action is highly visible and clearly indicates to the operator that the train must stop. It demonstrates the use of an accepted visual signaling technique that can be seen from a distance, ensuring that the train's crew has enough time to react appropriately.

Other options offered might not be as effective or recognized methods for stopping a train. For example, standing still and holding up a light may not gain the attention needed if the light is not easily distinguishable or if visibility is poor. Waving arms above the head may not communicate the urgency of stopping, as it could be interpreted in various ways. Lastly, using a loud horn sound does not constitute a visual signal, which is crucial for communicating effectively with the train operator, especially in situations where sound may be drowned out by the noise of the train or surrounding environment. Thus, only the action of moving an object across the track serves as a clear and established signal for stopping a train.