Shadow of communism at University of Chicago

According to this NPR story, the sculpture titled Dialogo on the University of Chicago's campus contains a hidden message.



Supposedly, every year, on May 1, at noon, it casts a hammer-and-sickle-shaped shadow:



As the sculptor Virginio Ferrari confesses, the effect was unintentional, although he enjoys the humor in it. I believe him because he could have done much better than the rather unrealistic version of the Soviet symbol.

Question: Do you know of a sculpture with an unmistakably intentional elaborate hidden message in its shadow that appears on a specific day of the year?