What signal should be shown during the night to indicate a bad or dangerous landing area?

The correct signal to indicate a bad or dangerous landing area at night is the steady red light. This is widely recognized in maritime navigation and safety as a warning to vessels or aircraft that they should avoid that area. A steady red light serves as a clear visual cue that something is hazardous, whether due to shallow water, obstacles, or other dangers.

The other signals mentioned do not convey the same warning effectively. For instance, a flare or white light moving horizontally could imply that there is some form of activity or signal, but does not specifically communicate danger. Additionally, a firing green star signal is often used to indicate safety or good conditions, not hazards. Flashing white light can be confusing or interpreted in various ways, and is not universally accepted as a warning signal for danger in landing areas. Thus, the steady red light is the recognized and appropriate choice for warning of a dangerous landing situation.