|Can't see it? Look harder . . .|
Right off the top I have to say that this is probably my favorite TARDIS sighting of all time. Well, maybe right behind the MIT sighting, but it's incredible nevertheless.
Crafty_Tardis on LiveJournal (via TARDIS Newsroom, by the way) happened to be in Boone, North Carolina, where the American university Appalachian State is located. To make a short story shorter, I actually know where this is; I've been to this exact location twice, and I never noticed this! Perhaps that's because it's relatively recent, but I prefer to think there are some mysteries in the world left unsolved.
The story with this is simple: Appalachian State has two tunnels that run underneath the primary road in through the university, and students are always allowed to graffiti the walls as they please. It's quite a clever idea for the university, which lies in the empty and high-up Boone. There isn't much there, so it's hard to imagine what brilliant college kid decided to put this in the tunnel for everyone to see.
Now, that's art.