There is a park in downtown San Diego named “Fault Line Park.” It is split in two by a fault associated with the Rose Canyon Fault Zone. They are so proud of the fault that they have created a walkway on top of it and, on either side, is a huge mirrored ball.
The balls were installed exactly opposite each other, but the eastern ball is slipping southward, and the western ball is slipping northward. In the western ball is a hole through which you can look to see if the two balls still are lined up exactly.
They are right now since the park was built in 2014, and the slippage is only 1 mm/year.
Of course, I did take a selfie in each mirrored ball.