The "knife-hand" is the multi-tool gesture of the military. Actually, you can think of it as a Swiss army knife – pun intended.
The knife-hand is used in a plethora of ways ranging from administrative to instructional and even to gauge anger, according to Terminal Lance creator Maximilian Uriarte. "Never, anywhere in the Marine Corps, have I ever seen the knife-hand so flagrantly used. I always took note, however, that the higher the knife-hand is on the drill instructor, the more pissed off he is."