1. "Die, Bart, Die" (Bob: "No, that's German for 'The Bart, The")

2. "Ouch Man!" (Bart's head on a skateboard)

3. a skull and crossbones

4. "LUV" (on one hand) "HAT" (on the other hand - with a macron over the 'A')

The "LUV" and "HAT" tattooed across the knuckles on Sideshow Bob's hands are an allusion to the Charles Laughton directed 1955 thriller The Night of the Hunter, in which Robert Mitchum plays a psychopathic preacher who has "LOVE" and "HATE" tattooed on his knuckles.