20th anniversary of the Warsaw Pact.
Flags of the countries participating in the Warsaw Pact
The participating countries as displayed by the flags were (from top to bottom): Poland, the Soviet Union, Bulgaria, Czechoslovakia, East Germany, Romania and Hungary.
XX Rocznica podpisania układu Warszawskiego = 20th anniversary of the signing of the Warsaw Pact.
Find other Polish stamps commemorating Warsaw Pact anniversaries