We did this in Los Angeles a few years ago with statues of angels: you take a bunch of plain statues (in Boston's case, cows) and give them to artists so they can paint them with all sorts of different themes.

While on the Freedom Trail today, I saw a Ted Williams cow, three really creative Blue Man Group cows, and this Poker Stars cow! Since I'm on Team Pokerstars, I went a little nuts with my digital camera, but exhibited great restraint with my phone's camera.