Operating signals are a type of brevity code used in operational communication among radio and telegraph operators. For example:

• Prosigns for Morse code
• 92 Code: telegraph brevity codes
• Q code: initially developed for commercial radiotelegraph communication and adopted by other radio services
• QN Signals: published by the ARRL and used in Amateur radio
• R and S brevity codes: published by the British Post Office in 1908 for coastal wireless stations and ships, superseded in 1912 by Q codes
• X code: used by European military services in wireless telegraphy
• Z code: used in early radiotelegraph communication