I got some lovely lead crystal tumblers with green shield stamps. Later I met someone who worked for the company who told me everything was seconds. However, still happy and have all 6 to this day.
you got given them in places like petrol stations and stuck them in a book. Then you went to a "redemption centre" to get goods with your books. There were also pink stamps from another company if I remember rightly, but greenshield were the biggest.