In Catalonia, it’s a deeply entrenched tradition to make a very specific kind of addition to public Nativity scenes:
Statuettes of well-known people defecating are a strong Christmas tradition in Catalonia, dating back to the 18th century. Catalonians hide caganers in Christmas Nativity scenes and invite friends to find them. The figures symbolize fertilization, hope and prosperity for the coming year.
Via P.Z. Myers at Pharyngula, who points it out for his own doubtless nefarious purposes.