I love it when architects or other artists exhibit a sense of humor in their products. In addition to a design that seems to have a "tin-man" face on the corner protrusion of this building, a small frog appears to be bench-pressing the upper story. I am sure there are other examples but I have personally only discovered two--and both were in Europe. The other example is Gaudí's Park Guell in Barcelona. The park is full of little artistic riddles as in "One of these (columns, windows, sections of a wall) is not like all the others..."
Kent Pendleton, an artist who painted diorama backgrounds in Denver's Museum of Nature and Science from 1971 to 1983 and from 1989 to 1995, "signed" five of his backgrounds by painting small hidden leprechauns who appeared to be peeking through the foreground plants. In what he originally thought was to be his last diorama in 1983, he painted one waving goodbye. When six years later he returned to paint more dioramas he added two more leprechauns. My husband, a volunteer docent who gives diorama tours at the museum--and carries in his head a passle of facts about the animals, the habitats, the adaptations of each bird and mammal depicted, says the most common question is: "Where are the leprechauns?"
I'd love to hear about other examples of artists displaying a subtle sense of humor in their works.