z flag
One of the international maritime signal flags. It is a square divided diagonally into four triangles, colored yellow, blue, red, and black.
It represents the letter Z when communicating by individual letters. Combined with four number flags, it represents the time in UTC. On its own, it may mean "I require a tug" or "I am shooting nets".
The Z flag is of special significance in the context of Japanese naval history due to its role in the Battle of Tsushima where it was raised on the flagship Mikasa. In this battle, the Z flag was understood to mean, "The fate of the Empire rests on the outcome of this battle. Let each man do his utmost".