1. Document of value comprising: at least one window area; and a polarization element disposed in the at least one window area; wherein, the polarization element rotates a plane of polarization of a linearly polarized light beam passing through the at least one window area, by a pre-defined angle, and wherein the angle is defined so that a plane of polarization of a linearly polarized light beam passing through window areas of several of said documents of value lying on top of the other is rotated by a corresponding multiple of the angle, and the polarization element is an element, which, induced by at least one of an outside electrical and magnetic field, rotates the plane of polarization of the polarized light beam passing through the associated window area by the defined angle.