Earlier quoted context omitted.
I suppose it would count as harassment, but that's because it'd be done to a person. I don't think it's possible to harass a computer program. If we ignore the harassment side of it, then I don't know what law it breaks, if the object can be trivially removed by the driver.
Criminal law - mischief - which generally includes altering of property and isn't limited to damage or destruction of property. Common law - tortious interference - if the vehicle is a taxi being summoned by a customer, and it cannot fulfill the contract because of the interference of a third party intentionally preventing its movement.
Tortious interference, as the name implies, is a matter of civil courts and could open up the person doing it to being sued, depending on the circumstances under which it happens. It doesn't mean they're breaking any laws.