If a signal is improperly displayed or absent, how must the signal be regarded?

The correct choice emphasizes the importance of safety and caution in railway operations. When a signal is improperly displayed or absent, it should be regarded as showing the most restrictive indication. This means that the train crew must assume the worst-case scenario in order to prevent potential accidents or hazards.

By treating the signal as the most restrictive, the crew is most likely to take appropriate precautions, ensuring that they proceed with maximum vigilance, such as reducing speed or stopping if necessary. This approach prioritizes safety and reinforces the principle that in situations of uncertainty regarding signal indications, erring on the side of caution is crucial.

This practice aligns with railway operations' overarching goal of maintaining safety and reliability on the tracks, particularly in situations where signals may not be functioning correctly or are ambiguous.