As Market Street art-washes its empty storefronts with murals today, the SFBT reports on interventions in Union Square, where the bombed out economy has driven out many a retailer. Empty storefronts are now getting filled in with seasonal pop-up stores, but the season also has a little something for us building fetishists: architecture displays. Brand + Allen, Charles Bloszies Broszies Architect, Fee Munson Ebert, and Gensler will be setting up displays in five empty Union Square spots by Nov. 11. (Gensler will have two.)