Flag are used for signalling purpose.Various Flags are used as a way for marking the Army Vehicles while moving in a Convoy.
The blue flag on the jeep indicates convoy commander’s vehicle.
First Red flag on the vehicle indicates the starting point (the First Vehicle) of the convoy and the last red flag on the vehicle indicates the end of the convoy (Last Vehicle).
Indian Army: Red Flag may be used to indicate presence of Explosives/Arms/Ammunition on the Vehicle.
Red flag can also mean as a metaphor, a sign of a problem requiring attention. It may also be flag of any regiment of Army. Like this one is of 3rd infantry.