If the player is facing 0 degrees (north), then this will do NOTHING.
If the player is facing 90 degrees (east), then this will make him bank 90 degrees to his left.
Kronzky
An in-depth discussion on the concept of vectors is available here.
Str
Command can be also used to rotate camera in all three axis (which also mean it is possible to set camera bank).
Killzone_Kid
It is possible to change both pitch and bank of an object (surfaceNormal application for instance).
Assuming an ammo box in the following example is facing North (default direction is 0):
_ammoboxsetVectorUp [0, 1, 0]; // box is pitched 90 degrees forward_ammoboxsetVectorUp [1, 0, 0]; // box is banked 90 degrees to the right
However the above will stop working as soon as you attach the box to something. The following trick however will work in this case:
_ammoboxattachTo [player, [0, 2, 1]];
_ammoboxsetVectorUp [0, 0.99, 0.01]; // box is pitched ~90 degrees forward_ammoboxsetVectorUp [0.99, 0, 0.01]; // box is banked ~90 degrees to the right