Interesting. This is just a guess, but in the event one needs to engage military aircraft with a 5.56mm rifle it could be a sighting guide. Judging by the angle of the line from the rear to front of the magazine, you would aim the helicopter line at an incoming helicopter. You would be shooting "high", but that would give the rounds time to cover the distance between you and a speeding aircraft. The airplane line is lower, forcing the muzzle higher, thus making you lead the aircraft even more.Does anyone recognize the airplane and helicopter symbol ??