What signal is included among the communication methods of a watchman?

The correct answer highlights that watchmen use a variety of signals to communicate effectively. Visual and audible signals encompass both physical gestures and sound-based communication, which are crucial for ensuring safety and coordination, especially in operations involving trains.

Visual signals can involve hand movements or flags, which provide clear instructions that can be seen from a distance, while audible signals include the use of whistles or horns to alert nearby personnel or to convey specific messages that require immediate attention.

While foot signals and whistles are indeed types of signals, they represent only a subset of the broader category of visual and audible communication methods. Radio messages, although part of modern communication, may not always be available in all settings or circumstances related to watchman duties, making them less inclusive compared to the comprehensive nature of visual and audible signals that can be used in diverse situations.