A while ago, I promised that I would graffiti Pearson's Product Moment Correlation Coefficient in Bournemouth. It is most certainly clever, although very complicated.
Remembering my promise, I set off for Boscomebe pier, beneath which is a graffiti hot spot as there always are under piers, with a large lump of chalk and wrote this:

I also wrote the formula for a circle while I was there, because it was the most clever thing I could remember at the time (I was having a dull moment, obviously).


I then left the pier and my equations behind to confuse the next dull person who comes along to write the same old dull graffiti as usual.