You're strolling around outside on your lunch break when, all of a sudden, a bird lets loose above you, depositing a messy smear of droppings on your head. At first glance, this might sound like the start of a really bad day, but superstitious types believe it's actually a sign of luck. Even better, you don't have to let the mess (which some people use as skin treatment!) linger; you can safely clean the droppings off without wiping away your newfound luck – unless, of course, you're on a ship. Sailors believe that bird droppings should never be removed from the vessel until after the next rainstorm, which will probably take care of most of the cleanup anyway [source: Martinelli].
While most superstitions about bird droppings are positive, some older British tales warn that if the droppings come from a rook, it's actually a punishment rather than a blessing. Getting bombed by the droppings of a rook is penance for not wearing new clothes on Easter [source: Tate]. Maybe it's time to invest in a new Sunday suit.