What additional signal is exhibited by an air cushion vessel operating in non-displacement mode?

The correct additional signal exhibited by an air cushion vessel operating in non-displacement mode is an all-round flashing yellow light. This signal is specifically designated to indicate the unique nature of air cushion vehicles, which do not operate like traditional boats or ships that sit in the water. The all-round flashing yellow light serves as a visual cue to other vessels that the air cushion vessel is not in displacement mode, helping to prevent collisions and ensuring that operators are aware of the vessel's operational status.

Additionally, this signaling is crucial for maintaining safety on the waterways, as traditional signals used by displacement vessels may not accurately communicate the maneuverability and travel characteristics of air cushion vessels. The other answer options do not correspond with the recognized signals established by maritime regulations for this type of vessel in that operational mode.