The mockingbird in TKAM is the ultimate symbol of innocence. As Atticus told Jem and Scout, "Shoot all the blue blue jays you want, if you can hit 'em, but remember it's a sin to kill a mockingbird." People can interpret this in many different ways, and they could come up with several different meanings. I believe that Atticus is telling them that you can kill the ones who have committed a crime, bluejays, but do not kill those who are innocent, mockingbirds. Scout is taking this information from Atticus and applying to everything like the mockingbirds, Arthur "Boo" Radley, and Mr. Dolphus Raymond.