33 CFR 87.01 – Need of assistance
The following signals, used or exhibited either together or separately, indicate distress and need of assistance:
(a) A gun or other explosive signal fired at intervals of about a minute;
(b) A continuous sounding with any fog-signaling apparatus;
(c) Rockets or shells, throwing red stars fired one at a time at short intervals;
(d) A signal made by any method consisting of the group . . . – – – . . . (SOS) in the Morse Code;
(e) A signal sent by radiotelephony consisting of the spoken word “Mayday”;
(f) The International Code Signal of distress indicated by N.C.;
(g) A signal consisting of a square flag having above or below it a ball or anything resembling a ball;
(h) Flames on the vessel (as from a burning tar barrel, oil barrel, etc.);
(i) A rocket parachute flare or a hand flare showing a red light;
(j) A smoke signal giving off orange-colored smoke;
(k) Slowly and repeatedly raising and lowering arms outstretched to each side;
(l) A distress alert by means of digital selective calling (DSC) transmitted on:
(i) VHF channel 70, or
(ii) MF/HF on the frequencies 2187.5 kHz, 8414.5 kHz, 4207.5 kHz, 6312 kHz, 12577 kHz or 16804.5 kHz;
(m) A ship-to-shore distress alert transmitted by the ship’s Inmarsat or other mobile satellite service provider ship earth station;
(n) Signals transmitted by emergency position-indicating radio beacons;
(o) Signals transmitted by radiocommunication systems, including survival craft radar transponders meeting the requirements of 47 CFR 80.1095; and
(p) A high intensity white light flashing at regular intervals from 50 to 70 times per minute.