Why did Brecht use placards and signs in his theatre?

Brecht used placards and sings in his theatre to provide the audience with information about the play, to remind the audience that they were watching a play, and to break the illusion of reality. By doing this, Brecht hoped to alienate the audience from the play, and to prevent them from becoming emotionally involved in the characters and the story. This alienation effect is designed to make the audience critically reflect on the play, and to see it as a critique of society.