Writing on the Wall

Saw the Rosetta Stone at The British Museum, with which decipherment of hieroglyphs was made possible. It had a decree written 3 ways.

The decree was written on a wall. I wonder what encoded decrees are written on our walls. Banksy does some pretty good code. I got his book for a friend this week. I felt like I should have got a set of stencils and can of spray paint instead.

Why don't people write on pavements or roads? There's more of them than walls, more horizontal space than vertical...and easier to write on too.