A flare pistol is used at the start of the mission "Suffer With Me" by a PDF soldier, when Woods and Mason attempt to pass the checkpoint. It cannot be picked up or examined closely, as it vanishes when the soldier is killed. Like all scripted items, it is classed as a prop instead of a weapon in game.
A PDF soldier raising his M8 Flare Pistol
Call of Duty: WWII
A flare pistol appears as a memento that can be collected in the mission "Death Factory". In the level, flare guns are used by the Wehrmacht and Waffen-SS soldiers.