The first thing that comes to mind here is the enormous red bullseyes that Target puts on top of all of its stores. They're visisble from airplanes and satellites, but their symmetry would make them less useful for calibration.
That's a brilliant move on Target's part-- how easy must it be to find your nearest target on Google/Bing/Etc Maps? Pretty forward thinking of them, if you ask me...
An example: http://craphound.com/images/googleeasrthad.jpg