Stamp International set of 8 postcards in envelope

A stamped brown envelope containing 8 cream-coloured A6 postcards; the picture side of each card features a white rubber-stamp of the word ‘secret’, each card in a different typeface and language (English, German, Spanish, Hungarian, Arabic, Japanese, Hebrew, and Russian), the flip side is the same for each card: printed in black are lines for the stamp and address, publication details and all 8 stamps in miniature, Köln 1980 NB: Envelope slightly creased + some edges worn, but overall in good condition.