Is this illegal or can i do this?

everytime someone parks at our house we don;t even know them they park their stupid car in our stalls. we live in a 2 story house we own the land and house and they keep parking their cars here. We have a ton of no trespassing signs and all that and my grandpa knows that people keep parking at our house freely they dont even pay us yet he is toos cared to do something but can we fk up their car as a warning? maybe like key the car or smash out the windows or something honestly it is tresspassing im just wondering if thats legal otherwise i will ust start calling tow trucks.