Bug
We watch as Maude peels out of the church in her Volkswagen Beetle after meeting Harold at a funeral. This is a symbol of her character being someone who is not normal compared to what is expected by people in society. Thus, she is turning a stereotype on its head.
Pistol
Harold loads a pistol while going through a dating questionnaire with his mother. He shoots himself, and his Mother doesn't bat an eye. This is a symbol that she knows her son has an obsession with pretending to kill himself, never actually doing so.
80
Maude takes an overdose of sleeping pills once she turns 80. This is a symbol of her seriousness of dying at 80. She does what Harold has only pretended to do the entire film.
Funerals
Harold and Maude meet at a funeral for someone whom neither knew. This is a symbol that each of these characters are obsessed with death, though for very different reasons - as Harold came after witnessing his mother faint as she believed he was dead. For her part, Maude is fixated on death because she is ready to die once 80 comes for her.
Overboard
Harold's car goes over the edge of the cliff, but we see that he is not in the car. This is a symbol that Harold is now someone who seeks to live life rather than constantly remaining obsessed with death.
