The signal flare (煙弾 Endan) is a common tool used in the military by the Garrison and the Survey Corps. The signal flare has a variety of uses, depending on the mission and brigade using them.

While the signal flare has many uses, its main purpose is long distance communication. The Garrison 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 in the presence of Titans) to the rest of the legion. One improvisational use is to use them to conceal allies from enemy sight or to stop fast moving Titans.

The ammo comes in pre-loaded barrels that are locked into place on the pistol. After being fired, the barrels are discarded and replaced before being capable of use again. There are various types of ammo and usage depends on the mission and message at hand.
The ammo the Garrison uses is the following:
  • Red: Mission failed.
  • Yellow: Mission successful.
The ammo the Survey Corps uses is the following:
  • Red: Titan spotted. (Used in order for the squad to avoid the Titans)
  • Black: Abnormal Titan spotted.
  • Purple: An emergency of some kind. (someone is grabbed, etc.)
  • 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.
  • Acoustic: While leading and abnormal Titan through the Titan Forest, Gero used a special shell that emitted a high-pitched noise.