International Code of Signals

These are a set of 39 flags, 26 letters, 10 numbers, 3 substitute flags and one answering pennant. They are used by ships at sea to indicate various conditions of the ship and the activities it is engaged in. Examples of this would be if a vessel had a diver down and was warning other nearby ships to stay clear.

• Answering Pennant: used to indicate that the signal has been received.
• Substitute Flags: these are used in a situation where the vessel needs to show more than one of the flags already used. For example if the ship wanted to display the flags A D E D, it could display them using A D E [second substitute], indicating to repeat the second flag there.

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