Code of Federal Regulations Title 33. Navigation and Navigable Waters § 33.87.01 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:

(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.