Well-placed sources at the Art Institute of Chicago reported Tuesday that the employees were bracing for an imminent encounter with a large group of identically clad people walking toward the building behind someone waving a purple wooden stick. The groupwhose members all wore shirts featuring a stylized bird logo that could represent a summer camp or religious youth groupbegan assembling approximately 40 yards from the entrance, causing museum employees to rush to assigned stations from which they could ensure no one would block hallways, loiter in bathrooms, or touch paintings. 'Heads up,' floor manager Carla Ellis said. 'It looks like they just got off a bus. I think they're from out of state. Here we go!' As of press time, the group was still dawdling 20 feet from the entrance, with at least one person in a wheelchair, and it was surmised that its members were either foreign tourists or a special-needs class. 