A hand signal used between Spartan II's in Halo, used to signify a smile in lieu of a real one, which can't be seen due to the Spartans' visors. Having grown up as soldiers, the Spartans kept their emotions to themselves, always controlling "bursts of emotion". The closest thing to an emotional symbol is the "Spartan Smile," used in place of a smile. The Smile consists of a quick swipe across one's own faceplate or a teammates with two fingers.
"What was that?"
"I think it's called a Spartan Smile. Y'know, since they can't see each other's faces, they've got a symbol for it instead."