April Fool's Day! Fish are a sign of good luck, and so are black cats. It used to be traditional to send postcards of Fish on April Fool's Day. In Italy, France, Belgium, The Netherlands, and French-speaking areas of Switzerland and Canada, April 1 tradition is often known as "April fish" (poissons d'avril in French, aprilvis in Dutch or pesce d'aprile in Italian). As a prank, friends attempt to attach a paper fish to the victim's back without being noticed. Such fish feature prominently on many late 19th- to early 20th-century French April Fools' Day postcards. Many newspapers also spread a false story on April Fools' Day, and a subtle reference to a fish is sometimes given as a clue.