This is not my kingdom

I don't know most people in Chicago on an individual basis, but of all the people I don't know, my favorite Chicagoans are scavengers. They roam the alleys in beat up pickup trucks, with various kinds of makeshift walls extended above the bed.
They grab anything made of metal and anything with the possibility of value. They reduce the amount of garbage going to landfills and I thank them very much for doing this.
Driving the other day, passed one such truck with a hand-lettered sign nailed to the wooden side wall. It said:
This is not my kingdom.Just passing through.