I don't know why I love things like this so much. Maybe it is because it's unique, completely random, out of place, and interactive. It might even make you think. Maybe you just think "I don't get it" or "Why is this here?" but still you use your brain. It's a nice break from the mindlessness that occurs when you're walking down the same street you walk down everyday.
Check out the Urban Cursor! I don't think it's a form of advertisement but it's not a bad idea. Maybe Photoshop CS4 could advertise my having giant tools that manipulated the ground covered in chalk. Just a thought.