The philatelic exhibition BALPEX I in Gdańsk. The original stamp is an issue from 1954 commemorating the 500th anniversary of the recovery of Pomerania after the second treaty of Toruń (see Fischer 733).
500 lecie powrotu Pomorza = 500 years of the recovery of Pomerania.
BALPEX = Baltimore Philatelic Society.
Peace of Toruń 1466 (Second Peace of Thorn)
Fischer 974 FDC