Abstract: A mailer for use with computer printing techniques. The mailer utilizes die-cut window envelopes provided with a transparent window web an undersurface of which is coated with a chemical composition. A sheet contained in the envelope and visible through the window is coated on its surface presented to the window with a second, different chemical composition. The coating compositions are characterized in that impression of impact printing forces against the window web and applied therethrough to the underlying coated sheet produces impact-pattern-correlated visual imprints on the envelope-housed sheet, the imprints being clearly viewable through the transparent web of the envelope window.

Abstract: An invalidating marking appears on photoreproductions of security documents such as checks, bonds, stock certificates, lottery tickets, and currency. The invalidating marking is disguised on the original by use of disguising markings and printing the invalidating mark and the background with different line screen frequencies.