Doesn't it depend where the obstacle is, though? I'm assuming these are cars parking on the road, or at least a shoulder or driveway. If the cars are pulling up onto a front lawn and parking under the kitchen window of a house, that's entirely different. I'm pretty sure filling a traffic cone with concrete and placing it in a path a car is expected to drive on is going to get you in trouble anywhere. I doubt building a snowman with a stump or concrete core in the middle of a lawn on private property would get you in trouble in most places.