Territorial Pissings

I came home last night to find a tractor and some tree trimming machine in my field. I guess it's the county's machinery. No note was left asking me to leave it there on MY land. Maybe I shouldn't get so worked up about it but it's the principal of it. They drove through my back yard to get to some trees. I don't appreciate it. Maybe if they would have said "Hey man, is it o.k. if we park our stuff here?"  Does that mean I can use it?  It's on private property. They could brush hog my field and we'll call it even.