It's stamped on t-shirts, hats and even some people's bodies. It's a Chicago trademark, but what exactly does it mean?
Let's take things back to 1917. Chicago writer and poet Wallace Rice designed the flag. At that time, it only had two stars.
One to symbolize The Great Chicago Fire of 1871 and another to symbolize the Columbian Exposition of 1893.
In 1933, the city added another star to represent the "Century of Progress", a time when Chicago was the Country's second-largest city.
Then in 1939, another star was added to commemorate Fort Dearborn, which was originally destroyed in the battle of 1812.
There are three white stripes on the flag, which represent the north, west and south sides of the city.
The top blue stripe represents Lake Michigan and the north branch of the Chicago River. The bottom stripe represents the south branch of the river and the great canal.