What type of signal is used to indicate a vessel’s distress at sea?

A vessel in distress at sea uses red distress flares as a universally recognized signal to indicate an emergency situation. These flares are bright red in color and produce a significant amount of light, making them visible from great distances, even in poor weather or at night. The use of red is significant because it attracts attention and signals urgency.

Other types of signals mentioned, such as a green light, flashing white light, or yellow smoke signal, do not have the same established association with distress. Green lights are typically used for marking safe navigational points or indicating specific conditions, while flashing white lights might indicate varying statuses but are not recognized specifically for distress. Yellow smoke signals may be used for signaling but do not have the same urgency or recognition as red flares do in distress situations. Thus, red distress flares are the correct and standard method of signaling that a vessel is in distress.