Wearing a paper clip was a crime in Nazi-occupied Norway during World War II. German invaders had forbidden Norwegians from wearing lapel pins bearing the image or initials of King Haakon VII. Instead, defiant citizens began wearing paper clips. (Johan Vaaler, a Norwegian inventor, was widely credited with having invented the paper clip in 1899.) Clip-wearing came to mean "people joining against the forces of occupation." It could also get you arrested.
Source: 'The Evolution of Useful Things,' by Henry Petroski (Knopf, 1992), quoting from Nanna Segelcke's 'Made in Norway' (Oslo, Dreyer, 1990).
(c) Copyright 2001. The Christian Science Monitor