Not too long ago I started seeing these "Bombs" around Albuquerque. I had no idea what they were for so I went googling.
According to their website it's all for charity. "Help us support those most in need by voting for the charity of your choice! Winning charities will receive more than $80,000 worth of prizes from boomtime and its network of local businesses."(www.makeemboom.com)
You can vote for your local charity (and see the rest of the "bombs") here and you can find the "Bomb" locations here. If you click on the "Bombs" on the voting page your can learn about the artist of that bomb and the charity the bomb represents.