International Code of Signals
The International Code of Signals (INTERCO) is an international system of signals and codes for use by vessels to communicate important messages regarding safety of navigation and related matters. Signals can be sent by flaghoist, signal lamp ("blinker"), flag semaphore, radiotelegraphy, and radiotelephony. The International Code is the most recent evolution of a wide variety of maritime flag signalling systems.
A sailor on board a US Navy ship preparing a signal hoist
The Z flag is one of the international maritime signal flags.
The Z flag (upper left) is still flown daily from the signal yardarm of Mikasa, now a museum ship
Members of Shuken Kaifuku wo Mezasu Kai bearing the Z flag and the Rising Sun flag