Sets flag owner. When owner is set to objNull or any object other than a unit of class man or logic, flag is returned to the flagpole. A flag owned by a logic has no visual representation.
Since flags can not be owned by vehicles, use "flag setFlagOwner driver tank1" or "flag1 setFlagOwner tank1D" to assign the flag to the vehicle's driver. The second method will only work if tank1 is the name of a unit, not a variable refering to it. True for OFP&Arma