Forum checks (German: Forumscheck) were a form of hard currency in East Germany. By law all East Germans had to convert immediately any Deutsche Marks (and other western currencies) they possessed into Forum checks at the state bank in April 1979. A Forum check mark was worth 1 West German Deutsche Mark. Forum checks were accepted in Intershops as payment for western consumer goods and other products which were only available in Intershop. Foreign citizens could use western currencies in these shops.
References
Forum check Wikipedia(Text) CC BY-SA