Morse code

Morse code was a symbolic representation of the alphabet, in which letters were represented by a series of sonic bursts of varying lengths. These bursts were visually represented by dots and dashes. The code allowed for messages to be compiled, one letter at a time, and sent between any two parties who could understand it.

Luke Smith was proficient in the code. He once used his K9 dog whistle to send a Morse message to Clani, via Mr Smith. (SJA: The Man Who Never Was)