Communicating With Color: Maritime Signal Flags

We see it everyday: the street signs on the way to work, the menu at lunch, the countless websites visited over the course of the day, maps, charts and graphs,  all use color to communicate their meanings. And this has been going on for who knows how long. Now I’m wondering what the first known example of such a use of color really is. My guess is that it probably dates back much farther than we would think.

One example of using color to communicate that started back in 1857 are the international maritime signal flags. While only using red, yellow, blue, white and black, these flags communicate special messages and have the capability to be used as individual letters to spell out any necessary messages from ship to ship while out at sea.

If you’re up for it, after studying up with this post jump over to the flag test to see if you’re ready for the open seas.

The Main Alphabet


I have a diver down; keep well clear at slow speed. With three numerals, azimuth or bearing.


I am taking in, or discharging, or carrying dangerous goods. (Originally used by the Royal Navy specifically for military explosives.)


Affirmative. With three numerals, course in degrees magnetic.


Keep clear of me; I am maneuvering with difficulty. With two, four, or six numerals, date.


I am altering my course to starboard.


I am disabled; communicate with me.


I require a pilot. When made by fishing vessels operating in close proximity on the fishing grounds it means: “I am hauling nets”. With four or five numerals, longitude. (The last two numerals denote minutes and the rest degrees.)


I have a pilot on board.


I am altering my course to port.


I am on fire and have dangerous cargo on board: keep well clear of me, or I am leaking dangerous cargo.


I wish to communicate with you. With one numeral, I wish to communicate with you by; 1) Morse signalling by hand-flags or arms; 2) Loud hailer (megaphone); 3) Morse signalling lamp; 4) Sound signals.


In harbor: The ship is under Quarantine.
At sea: You should stop your vessel instantly. With four numerals, latitude. (The first two denote degrees and the rest minutes.)


My vessel is stopped and making no way through the water.


Negative.I am dragging my anchor.


Man overboard. (often attached to the man overboard pole on boats). With a sinister hoist, the semaphore flag.


The Blue Peter.
In harbor: All persons should report on board as the vessel is about to proceed to sea.
At sea: It may be used by fishing vessels to mean: “My nets have come fast upon an obstruction”.


My vessel is “healthy” and I request free pratique.


The way is off my ship. With one or more numerals, distance in nautical miles.


I am operating astern propulsion. With one or more numerals, speed in knots.


Keep clear of me; I am engaged in pair trawling. With four numerals, local time. (The first two denote hours and the rest minutes.)


You are running into danger.


I require assistance. With one or more numerals, speed in kilometres per hour.


I require medical assistance.


Stop carrying out your intentions and watch for my signals.


I am dragging my anchor.


I require a tug. When made by fishing vessels operating in close proximity on the fishing grounds it means: “I am shooting nets”. With one or more numerals, time (UTC). (The first two denote hours and the rest minutes.) (Origin of the phrase ‘Zulu Time’.)

The History of Signal Flags

The International Code of Signals has been in continuous use since 1857, when it was published by the British Board of Trade as a means of maritime communications. The original Code contained 17,000 signals using 18 signal flags, some of which were specific to the United Kingdom. The Code was revised in 1932 to include seven languages: English, French German, Italian, Japanese, Spanish and Norweigan. When the code was revised again in 1969, the revision included Russian and Greek, plus giving a complete meaning to each of the alpha-numeric nautical signal flags.
Reed’s Nautical Almanac

Check out the numeric and secondary signal flags at wikipedia.

header image by quinn.anya

Author: evad
David Sommers has been loving color as COLOURlovers' Blog Editor-in-Chief for the past two years. When he's not neck deep in a rainbow he's loving other things with The Post Family (, a Chicago-based art blog, artist collective & gallery.