Leave roofing nails on the ground where they park. Maybe put some sand in their gas tank :)
sugar in the gas tank will mess up the entire fuel line..try that one!! Or just egg their car. I know it seems childish, but let loose and have a little fun with it. Let your kids throw baseballs near their car! HEY its YOUR yard! "accidentally" key it as you go on your morning walk! haha!
You can't do anything, the street belongs to the city. Its a damn shame ain't it?
We have the same problem in this neighborhood and it is to bad the city owns the street because if I did a tow truck would be coming out everyday oh and there would be a sign "if you park here u will be towed ''.I can only dream...