Simple solution: Take all the snow you shoveled and put it back in that spot...covering their car.
Extra work, yeh, but satisfying.
My Dad had a neighbor park in the spot he dug out (2 foot snowfall) and he gave her the option.
1. Move your car now.
2. Move your car in the spring.
He told her he would put all of the snow back and then get the garden hose and it would be a solid block of ice.
She moved the car.