Why must the flight attendant ensure no red is visible on the overhead bin handle when closing it?

The necessity of ensuring no red is visible on the overhead bin handle when closing it primarily stems from safety protocols. A red marker typically indicates that the bin is not fully closed. If any red is visible, it signals to the flight attendant that the bin may not be securely shut, which could create safety risks during the flight. A properly closed overhead bin is crucial as it prevents luggage from falling out during turbulence or when the aircraft is in motion, thus protecting passengers and crew members. Therefore, confirming that no red is visible ensures the safety and security of all individuals on board, making it vital for flight attendants to check the overhead bin handles carefully.