What action must be taken when a blue signal is displayed?

When a blue signal is displayed, it indicates that work is being performed on or near a piece of equipment, and it serves as a warning to other train and track personnel. The primary action required in such a situation is to ensure that equipment is not coupled to or moved. This is important for the safety of those who are working in the area, as it prevents any unintended movement of the equipment that could result in serious injury or accidents.

The presence of a blue signal communicates to all employees that caution must be exercised, and that they should maintain a safe distance. This rule is in place to protect workers and maintain a safe work environment. Other options do not align with the protocol surrounding blue signals, as coupling or moving equipment could compromise safety, while ignoring the signal or assuming other equipment will obscure it contradicts the purpose of having clear signaling systems in place.