These are old French postcards for April 1, April Fools Day. The postcards usually include the words 1er Avril (April 1st) or Poissons d’Avril (April Fool). Other words on these cards often relate to expressions of love. Sometimes the cards just feature fish, with or without other words. Fish are featured because, in France and some other countries, the April Fool’s Day tradition is known as “April Fish.” The custom involves attempting to attach a paper fish to the victim’s back without being noticed.