Tamper marks. The traditional "lick to seal" envelope could be opened (as lore goes) over steam or on a hot plate. Visible pen strikes make it hard to re-seal i

Tamper marks. The traditional "lick to seal" envelope could be opened (as lore goes) over steam or on a hot plate. Visible pen strikes make it hard to re-seal it unnoticed by recipient. The only picture I found is this: https://coollib.com/i/39/408039/img_17.jpg https://coollib.com/i/39/408039/img_17.jpg an archive picture of a letter from out-of-favor Beria's henchman Abakumov to his boss. Dated 1952, so this practice must have been there for a while.