The black bird
Sadie's husband looks down upon a dead black bird shortly before she comes out to kill him. It is a clear representation of him and a foreshadowing of what's to come. The bird is on its back, in the same position he is about to be in while Sadie kills him.
Cody's drawing
Cody's drawing is a symbol that Sadie uses to remind herself why she's doing the job of a vigilante and reminds her of the revenge she needs to focus on. It represents comfort and helps her calm down during her panic attacks.
Anger
Anger is dramatically represented in the movie. The opening scene shows Sadie angrily punching the boxing bag, and later on she focuses her anger on the goal ahead. She encourages anger in abuse victims she helps as a form of therapy to be able to let the past behind.
