Apparently, the "Everything Must Go" signs are part of artist Nicolas Torres' rather brilliant Neighborhood Watch exhibit that's currently on display in Adobe Books' storefront windows. Torres' installation explores - and exploits - "the accretive motion of a city’s attempt to eliminate urban blight."
Well played, Torres. You've had us all scratching our noggins over this one. The exhibit runs through June 20, so go check it out and buy some books, of course!