International Code of Signals (ICS) - Flag Guide

Signal flags are used at sea for communication between ships while maintaining radio silence. Navy Signalmen transmit messages by hoisting a flag or a series of flags on a halyard. When communicating with other vessels, the International Code of Signals (ICS) is used. 


In ICS, individual flags can spell out short messages whereas a combination of flags can have a special meaning. The code / answer pennant precedes all signals in international code. Signal flags are sometimes also used to decorate ships during festivities.


All signal flags include one of three attachment methods:

1) Rope and toggle       2) Header and grommets       3) Brass snap and ring

     Header & Toggle                 Header & Grommets                       Brass Snap & Ring


There is a total of 40 flags in a set: 26 alphabet flags, 11 pennants (numeral flags) and 3 substitutes. Substitutes are utilized to repeat a previously used character without having to buy multiples of the same flag. The flags run from size 0 to size 14; the dimensions chosen are dependent on the height and length of the vessel, how much space is allocated for the signal flags, etc.


Signal flag size chart:

Size 0 Size 2 Size 3 Size 7 Size 10 Size 14
Flags 12x15in 18x24in 24x24in 36x36in 48x48in 48x72in
Pennants 8x24in 16x36in 16x36in 24x54in 32x72in 32x108in
Substitutes 8x16in 12x24in 16x28in 24x48in 32x64in  32x64in


The 26 alphabet flags:

International Code of Signals Alphabet Flags



The 11 numeral and code / answer pennants:

International Code of Signals Pennant Flags



The 3 substitutes:  

International Code of Signals Substitue Flags



Examples for using substitute flags to repeat a previously used character:

"ILL" Signal Flag "I" Signal Flag "L" Signal Flag Second Repeater
"NOON" Signal Flag "N" Signal Flag "O" Signal Flag Second Substitute  Signal Flags First Substitute
"BELL" Signal Flag "B" Signal Flag "E" Signal Flag "L" Signal Flag Third Substitute



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Flag Buying Guide

Boat Flag Buying Guide

Custom Flag Buying Guide

Hardware Buying Guide

Flag Etiquette

Glossary of Flag Terms