Distress signals are the internationally recognized visual and audio indications that a vessel or person is in grave danger, listed specifically in COLREGs Annex IV — distinct from, and complementary to, radio distress calls (Mayday) and digital GMDSS alerting.
Recognized Visual Distress Signals (COLREGs Annex IV)
- Rocket parachute flares or hand flares showing red light
- Orange smoke signal
- Rocket or shell throwing red stars, fired singly at short intervals
- Continuous sounding of a fog-signaling apparatus
- Flames on the vessel (as from a burning tar barrel)
- A square flag with a ball, or anything resembling a ball, above or below it
- Slowly and repeatedly raising and lowering arms outstretched to each side
- The distress signal SOS (by any method — Morse code, radio, or otherwise)
- The code flags “NC”
Why Multiple Signal Types Exist
Different signals suit different situations — a rocket flare is visible at genuine distance and works when no radio contact exists at all; the raised-and-lowered arms signal requires no equipment whatsoever and works ship-to-ship or ship-to-shore at closer visual range; SOS works across virtually any communication method available.
Distress Signals vs Mayday vs GMDSS Alert
These aren’t competing systems but layered options:
- Visual/audio distress signals (Annex IV) — work without any electronic equipment, visible/audible at range, used when other methods fail or as reinforcement
- Mayday (voice radio) — the standard verbal distress call, providing detailed information (position, nature of emergency, assistance needed)
- GMDSS digital distress alert (DSC) — automated, includes position data, alerts multiple stations simultaneously
A genuine emergency often uses several of these together — a GMDSS alert plus a Mayday call plus visual flares if a vessel is nearby, rather than relying on just one.
Misuse Is a Serious Offense
Firing a distress signal, or making a false distress call, when no genuine emergency exists is treated as a serious offense internationally — these signals trigger real search and rescue responses, diverting resources and genuine risk to rescuers, and false alerts are investigated and penalized.
Exam Relevance
The full list of COLREGs Annex IV distress signals, and how they complement Mayday/GMDSS procedures, are core Safety and Navigation topics in deck officer competency exams.