Downtown Los Angeles has no shortage of street art, from the historic murals that grace freeway walls and aging brick buildings to the flowering graffiti and more graphical works from the likes of Shepard Fairey. Some of it is political. Some of it is social commentary. Much of it is serious. But over the past several weeks, downtown has been the site of a decidedly lighter form of guerrilla street art that has generated much buzz and debate over its deeper meaning. It started in May when Calder Greenwood and his partner, known only as Wild Life, began collaborating on a series of papier-mache installations. The goal, Greenwood said, is to get people to notice things they pass every day but never see.