(under subclass 80) Envelope closures having sealing-flaps which are printed with or have concealed in them a soluble dye which spreads if the envelope is tampered with by the use of water or steam.
SEE OR SEARCH CLASS
283, Printed Matter,
72+, for safety paper or printed matter having fraud preventing characteristics wherein there are structural features other than the coating or impregnant.
427, Coating Processes,
7, for processes of coating wherein the product produced includes a fraud or tamper detecting feature.
428, Stock Material or Miscellaneous Articles, 199, for a single or plural layer web or sheet including a
developable image or soluble portion which would indicate an attempt to tamper therewith (e.g., safety paper), and subclasses 915 and 916 (cross-reference art collections for products which are made to detect attempts at tampering.
