Chicago Fire Department officials say the fire began in the sign and appears to be electrical in nature. It was struck around 5:30 a.m. No injuries were reported.
During the fire, part of the sign broke off and crashed to the ground.
A theater spokesperson said no one was in the building at the time of the fire, and that the fire did not spread into the building. All performances will proceed as normal.
The fire was caught on cell phone video by radio DJ Brian Sherman while on his way into the 101 WKQX station.