Explain the role of the fasten seatbelt signs during flight operations.

The fasten seatbelt signs play a crucial role in maintaining safety during flight operations. The primary function of these signs is to indicate to passengers when they must remain seated with their seatbelts fastened. This is particularly important during instances of turbulence, takeoff, landing, and other phases of flight where sudden movements are possible. When the signs are illuminated, it serves as a clear and authoritative message from the flight crew that compliance is necessary, helping to prevent injuries caused by unexpected turbulence or maneuvering of the aircraft.

While other options may hint at related functions of cabin procedures, such as allowing movement around the cabin or serving meals, these actions must always fall within safe operational parameters guided by the status of the fasten seatbelt signs. This highlights the signs' primary function, which is to ensure the safety and security of passengers on board.