What did it mean when the flag on top of shakespears flag was flying?

When the flag on top of Shakespeare's Globe Theatre was flying, it indicated that a play was being performed that day. The color of the flag signified the genre of the play: a white flag for comedies, a black flag for tragedies, and a red flag for histories. This system allowed the public to know what type of performance to expect before purchasing a ticket. The use of flags was an effective way to attract audiences during that time.