Tamper resisting holographic security seal

A tamper resistant security seal comprising a laminate having a transparent carrier layer;

• an optical, diffraction pattern defining layer;
• and an adhesive layer for adhering the seal to a substrate, wherein an optical pattern defined by the optical, diffraction pattern defining layer is visible from outside the laminate, and wherein an attempt to tamper with the seal will cause an irreversible change in the optical pattern characterized in that the optical, diffraction pattern defining layer is formed by a polymeric layer permanently bonded, directly or indirectly, to the transparent carrier layer, such that any attempt to delaminate the carrier from the optical, diffraction pattern defining layer will irreversibly damage the optical pattern;
• in that the adhesive is a pressure sensitive adhesive;
• and in that the laminate is such that a reduction in temperature below O.degree. C. will cause one or both of (a) a contraction of the carrier layer more than the other layers such that there is an irreversible change in the optical pattern, and (b) an irreversible change in the optical pattern upon attempted removal of the seal from a substrate, subsequent to such a temperature reduction.