In 2004, La Poste's museum participated to the Nuit Blanche ("Sleepless Night") : one of the many contemporary art manifestations, organized during a saturday night in Paris. Aside a large boredom (cetainly due to my lack of appreciation for some arts...), I got this stationery that the visitor could decorate before sending :
The stamp is a Marianne du 14 juillet, in use at that time. Its creator, Ève Luquet, was the first woman whose project became a definitive stamp in France. On the zoom, you can see in white-pale rose the trace of the two phosphor bands needed for the mechanical sorting of mail (see TimbresPhospho's blog in French to know more about these phosphor bands on stamps of France).