- Morse Code
- The sequence of short and long signals of lights or sounds used in communication
- Phonetic Alphabet
- A list of code words assigned to letters in the latin alphabet allowing for clearer voice messages by radio or telephone
- Semaphore Flags
- Used for communication that involves a signalman positioning their arms in a fixed position to encode and transmit a message
- Signal Flags
- Flags to represent individual letters of the alphabet to aid in signalling to or from sailing vessels