Flare Gun Location Battle description

Flare gun is a gun used to give signals and ask for supplies. The received signal will be responded to by the arrival of the aircraft that will drop the supply in the battle arena.

Some battle locations:
Erangel (Alpha Map) a Russian map.
Miramar (Map 2) a Central America sand map.
Vikendi (Map 3) an Adriatic island snow map.
Sanhok (Map 4) a Southeast Asian forest map.
Erangel (Remastered)

Where is the flare gun located? This is important because the supply is very supportive of battles ranging from weapons and armor. Are there any secret locations? Check in this application.