Question: what are two symbols in to kill a mockingbird?
Answer: Mockingbird. Only do good things for society, so hurting or killing one is a sin, represents Boo and Tom and maybe Atticus, but it is more likely that he is just the one who said it.
Camellias. courage, forgiveness.
Knothole (and its contents) ... 
Tom Robinson. ... 
Red geraniums. ... 
Boo Radley. ... 
Atticus. ... 
Blanket.