Signs
When we saw a pair of busted port-o-potties by the side of the road we said, "Oh shit!" and laughed for a while in the car.
It was the end of the road for the sibling road trip, and the end of the road was big and beautiful, because the end of the road was in the middle of New Mexico, where we found one final sign to let us know the road was good.
But we didn't need signs to know that.