pavement symbols

this paved pathway is on my shortcut route to/from work. lo and behold, a new artistic alphabet has appeared. i looked around, thinking maybe there would be some sign indicating why this appeared here this week. it wasn't here in 2011 and yet there was always the possibility of it being drawn/spray painted back then. in my view, any blank wall or expanse of smooth pavement is a canvas awaiting an expression in chalk, aerosol, or ink. it's fascinating to me to imagine the impetus that gives way to art being inscribed at this moment and not at another--particularly in locations that are in public space(s). what catalyzes an individual to just go ahead and fulfill the promise, act on the instinct, scratch an itch?