Secure Seals. 12 per pack. Secure Seals are tamper evident seals that can be used on important, confidential or sensitive document. Perfect for protecting your post against tampering. Secure Seals are easy to use self adhesive squares; simply stick to the seal of an envelope or document; once the seal is broken, the word "void" appears. Size: 35mm x 35mm. Ideal for envelops, parcels, sensitive documents, internal mail, wage packets and other confidential items.