Which of the following is a sign that employees may be working on or under a train?

The presence of a red lantern displayed is a clear indicator that employees may be working on or under a train. A red lantern specifically signifies a warning to approaching trains, alerting them to the potential hazard ahead. It serves as a crucial safety measure, ensuring that train operators are aware that there are workers in the vicinity of the tracks, thus prompting them to exercise caution or halt until it is safe to proceed. This visual signal is vital for maintaining safety protocols in train operations and preventing accidents.

In contrast, a green lantern generally indicates that it is safe to proceed, and a white flag is often used to signal a slow or stopped train but does not specifically alert against potential worker hazards. The yellow caution sign is more indicative of general caution but does not convey the specific message of workers’ presence like the red lantern does. Thus, the red lantern stands out as the correct sign for signaling that employees may be in the area of the train.