When must a train be prepared to stop at the Working Limits Stop Sign?

A train must be prepared to stop at the Working Limits Stop Sign when approaching from any direction because the sign indicates an area where construction or work activities are taking place, requiring increased caution and the potential for hazards. This rule applies regardless of whether there are passengers aboard or if a signal is visible, as the priority is always the safety of the crew and any work being conducted in the area. It ensures that train operators are aware of the need for caution and can respond appropriately to any situation that may arise. Therefore, the correct response highlights the universal requirement for trains to be ready to stop before proceeding through these potentially hazardous zones.