In the early days of aviation, airports would paint their name in big letters on the roof of the terminal. Incoming aircraft had few navigational aids at the time, so turning the territory into something resembling a map was a clever expedient.
I like the fact that nobody on the ground ever saw the sign. It was a well-targeted sign, visible only to the eyes that needed to see it.
Now we all have eyes in the sky. We travel by air more these days, but beyond this, Google and other mapping services have given us a permanent seat in the sky. Deskbound archaeologists can discover previously obscure ruins. But what about signage for the Google Earth set?
It’s arrived in the form of rooftop QR codes. Want to know what company is based in that building? Just scan the code. You’ve heard of cornfield mazes. Now meet the QR cornfield. We should carve a giant QR code onto the moon so that approaching spaceships could scan it. But what to link to? Assuming visiting aliens could decipher the message (and why not? they’ve got a freakin’ spaceship already), it would be good to link them to a video of earth music. Perhaps something by Rick Astley.
Rambles Blog at Star Chamber 
In a similar vein, with Google Maps I can discern the path of long demolished railroads – I have an ancestor in Monmouth County, New Jersey, who was a station keeper on the old Southern New Jersey Railroad in the 1800s. The track is long gone, but the right of way is still visible on Google.
I wonder if there’s path through Georgia visible from the sky made by Sherman’s March to the Sea.
excellent!
Sherman was as bad as an asteroid, so it wouldn’t surprise me.
Regarding old railways, the fact that many of them have been converted into bike paths and hiking trails leads to a curious result. In the old days, trains had privileged access to the very best route into a city. Now you have these well sited and smoothly graded trails filled with bikes and joggers, while the cars get the second best route.