Jokes with number stamps

It is often claimed by people who do not care for the hobby of philately that stamp collectors are boring and stuffy. However, the fact that collectors can also play and appreciate a joke is evident from, for example, the 'creative' sticking of stamps. As an example, consider an envelope sent on May 10, 1969. The National Philatelic Exhibition took place at the Houtrust Hall in The Hague from May 8 to 11. A temporary post office was also present. A collector used an envelope from the exhibition and affixed a number of numeral stamps to it: an 8-cent stamp for the day, two 1-cent stamps for the day 11, and a 5-cent stamp for the month of May. The year was formed by a 1-cent stamp and three 6-cent stamps, with the first and third 6-cent stamps affixed upside down to form the number 9. In doing so, he recorded the period during which the exhibition was held. That this prank was repeated later is evident from the card made to form the date July 7, 1977. The 9 cent was not in Van Krimpen's assortment of numeral stamps, and therefore the 6 cent was pasted upside down here as well to form the year 1977. Collectors throughout the country will surely have made other combinations to create specific dates. Have you ever pulled such a prank yourself?