Apple's annual developer conference in San Francisco.
Apple Begins Decorating Moscone Center for WWDC 2013, 'Where A Whole New World's Developing'
The banner use the same color scheme as the WWDC invitations sent out in April.
MacStories has also shared a picture of workers installing WWDC graphics on the outside of Moscone.
Workers will continue installing graphics throughout the day and readers are encouraged to send their photographs to firstname.lastname@example.org.