Which signal indicates a vessel is in distress?

The signal that indicates a vessel is in distress is represented by the International Code Flag 'N' (November) over 'C' (Charlie). This signal is universally recognized in maritime communication and specifically conveys that the vessel is in need of assistance. The combination of these two flags clearly communicates an emergency situation to other vessels and to maritime authorities, making it an effective visual signal in distress scenarios.

Other signals exist, such as a solid white flag and an orange smoke signal, but they do not have the specific meaning associated with a distress call. The solid white flag typically indicates a request for a ceasefire or truce, while the orange smoke signal is often used for signaling or indicating position rather than explicitly indicating distress. A single horn blast is a sound signal that can indicate various things in maritime communication, such as warning or signaling intent, but does not specifically signify distress. Thus, International Code Flag 'N' over 'C' is the correct and recognized signal for indicating that a vessel is in distress.