Final answer:
The NO SMKG switch set to AUTO illuminates the no smoking lights typically during takeoff, landing, or when the seat belt sign is activated, to ensure passenger safety and compliance with regulations.
Step-by-step explanation:
When the NO SMKG (No Smoking) switch is selected to AUTO on an aircraft, the no smoking lights in the cabin will typically illuminate in response to certain conditions. These conditions often include when the aircraft is taking off, landing, or when the seat belt sign is activated. As part of standard safety procedures, the auto function allows the lights to automatically come on without manual intervention to ensure passenger compliance with no smoking regulations during critical phases of flight or when deemed necessary by the flight crew.