What is flag semaphore?

Flag semaphore is a visual signalling system in which a person holds a flag in each hand and positions the arms at set angles to spell out letters and numbers. It was widely used at sea for ship-to-ship communication.

How are the arm positions described?

Each arm points to one of eight positions around the body, like points on a clock or compass. A character is defined by the combination of where the two flags point, shown in the diagram as two lines from a central point.

How are numbers signalled?

There is no separate set of number positions. The signaller sends the Numerals sign, after which the positions for letters A through K stand for digits 1 through 0, until the Letters sign switches back.

Is the J position special?

Yes. The letter J shares its position with the Letters sign, which is used to switch back from numerals to letters. Context tells the reader whether a J or a mode switch is intended.

Is semaphore still used today?

It is largely historical, replaced by radio, but it is still taught for emergencies and ceremonial use, and remains part of scouting and naval training. Knowing the chart is useful for puzzles and signalling drills.

Semaphore Flag Alphabet Reference

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Semaphore flag alphabet reference

Flag semaphore lets two people communicate across a distance by holding a flag in each hand and positioning the arms at fixed angles. Each letter is a unique pair of arm positions. This reference shows a clear diagram for every character so you can encode or decode a message at a glance.

How it works

Imagine eight positions evenly spaced around the signaller’s body, like the points of a compass. Each arm can point to one of these positions, and a character is defined by the combination of the two arms. The system is built so that letters progress in an orderly way: A through G keep one arm pointing down and sweep the other arm around, then H onward shifts the base arm.

Numbers reuse letter positions. The signaller first sends the Numerals sign; after that, the positions normally meaning A through K stand for the digits 1 through 0. The Letters sign (which shares J’s position) switches back to ordinary letters.

Tips and notes

The diagrams are drawn as seen facing the signaller, so their right arm is on your left. Mirror the image if you are the one sending.
Because numerals borrow letter positions, always send the mode signs — a message read in the wrong mode turns digits into the wrong letters.
Semaphore is slower than Morse but needs no equipment, which is why it endured for line-of-sight naval signalling before radio.