What is the symbol of the book?

A mockingbird. Remember, it's a sin to kill a mockingbird.

A mockingbird is the symbol of To Kill a Mockingbird.

A mockingbird. That's why you read the book. The symbols are actually also, Tom Robinson, (a black man accused of raping a white man's white daughter), and Boo Radley, (a man who never comes out to say hello)