Clown Masks
As Arthur's descent into madness accelerates, clown masks become more prevalent in the film. We first see a clown face in the film at Arthur's job as a hired clown. After he kills the three men on the subway, citizens wear clown masks, which symbolize civil unrest and protests against the rich.
Guns
We first see a gun in the film when Arthur's coworker gives him one. As Arthur descends into madness and violence engulfs Gotham, guns—and gun imagery—pop up much more often (wielded by Arthur, protestors, and cops).
Blood Red Lips
When Arthur stands up on the hood of the cop car towards the end of the film, assuming the role of leader of the revolution, he notices his lip is bleeding. He smears the blood across his lips, as though it is clown makeup. This represents the way that violence and clown imagery are linked in the film.
Arthur watching his clip
Twice we see Arthur's face fall while watching the video clip of him bombing on a comedy show. First, in his mother's hospital room, he watches Murray introduce a clip of his comedy, and his face becomes filled with sadness and fear as he realizes the clip is being shown mockingly. Then, later, as Murray introduces him onto the show as a guest, he watches the clip again, his face sunken in anguish and humiliation.
