Signal Flags Activity

Stick figure sketches of a short haired person wearing red shorts on left and a long curly haired person in flower dress on right. The people are holding two ropes spanning between them. Each rope has four different signal flags.
Send your own messages using signal flags!

Long before radio communication, mariners used signal flags to communicate between ships. An international code still exists at sea today. Each flag stands for a letter or number. String multiple flags together and one can send a message as far as the eye can see. If flown by themselves, single signal flags can also mean special codes.

With the materials below, you can get started on two different activities: Activity 1: Decipher Signals and Activity 2: Print, Cut, and Create Messages.

4 rows of square flags each representing a letter of the alphabet or the numbers 0 through 9. Each flag has the letter or number and their phonetic name below them
International Code of Signals alphabet flags and number pennants. Print this key or use the gallery above to decipher messages.

Activity 1: Decipher Signals

Below are several messages encoded using signal flags. Use the online gallery above or the printable key to solve each message. The answers are in collapsible items that follow each code!

Three square flags in a row: A 4x4 checker flag of white and blue, a blue flag with a white square, and a white flag with a blue square.
Answer: NPS
Short for National Park Service.
5 square flags in a row: 1, 2 vertical halves, left white, right is red. 2, 2 horizontal halves, blue on top red on bottom. 3 and 4 are both 2x2 checkered with yellow and black. 5 is divided diagonally with yellow bottom left and red top right.
Answer: HELLO
How are you?
4 square flags in a row, 1 is checkered blue and white. 2 & 3 have red white and blue vertical bars, and 4 has half white and half red vertical rectangles.
Answer: NTTH
Radio stations have call signs used to identify them. This is true for television, FM radio, and even ships like USS Cassin Young. During World War II Cassin Young operated with the call sign November Tango Tango Hotel, or, NTTH.
6 square flags in a row: 1, red swallow tail, 2 & 5, half yellow & red divided by diagonal, 3, white with blue square, 4, red white & blue vertical bars, 6, checkered blue and white
Answer: BOSTON
Home to three National Park units.
1 blue pennant with white dot. 5 square flags follow: 1 and 5 white with blue square, 2 left white right red, 3 yellow with black dot, 4 blue with white square
Answer: 2 SHIPS
The Charlestown Navy Yard is home to two ships: USS Constitution and Cassin Young.
1 red pennant with white cross. 6 square flags follow: 1 blue box white middle & red square center, 2, white left red right, 3, white with blue swallow tail, 4, yellow & black checker, 5, top blue bottom red, 6 white with blue square
Answer: 4 WHALES
Between Boston Harbor and Cape Cod, the Stellwagen Bank National Marine Sanctuary is home to a wide variety of wildlife, including whales.

Activity 2: Print, Cut, and Create Messages

Using the files below, print out the signal flag sheets. Cut out each flag and arrange any number of them to form a message you want to send. You can glue your message to paper or even hang them on a string.

Boston National Historical Park

Last updated: March 30, 2022