Signal flare

The Signal Flare is a common tool used in the Military by the Stationary Guard and the Survey Corps. The signal flare has a variety of uses depending on the mission.

Uses
While the Signal Flare has many uses its main purpose is communication over long distances. The Stationary Guard uses it as a way to inform the higher-ranking officers how their mission is going while the Survey Corps uses it as a way to communicate (often presence of Titans) to the rest of the legion.

Ammo
The ammo used depends on the mission at hand. The ammo the Stationary Guard uses is the following:
 * Green - Mission started.
 * Red - Mission failed.
 * Yellow - Mission successful.

The ammo the Survey Corps uses for the 57th Expedition beyond the walls is the following:

A sound grenade was also used however its current use is unknown.
 * Red - Titan spotted.
 * Black - Deviant Type Titan spotted.
 * Purple - An emergency of some kind.
 * Blue - An order to retreat.
 * Green - Change direction of the formation: Fired by the commander in one direction to indicate a change in the direction, and then repeated by the relay soldiers.
 * Yellow - This lets everyone know that the mission has been terminated, be it successfully or failed.