Symmetry Operations
Non-translational symmetry operations include:

Rotation axis - labeled “N”, indicating a rotation of 360°/N. Thus a rotation of 180° is a 2; a rotation of 120° is a 3.
Notice that the “handedness” of the molecule does not change during the rotation operation, of course.

For a complete list of the symbols for crystallographic symmetry elements (like the double-headed arrow and the triangle in the above figures), go here.