In NZ (where I think this was taken - see the silver fern on the jersy in foreground and the anchor milk truck in background) the display on buses not in use alternates between "Sorry" and "Not in service". Sorry is quite possibly a coincidence.

My boyfriend had NEVER played an FPS in his life, stumbled n00bishly through L4D on Easy, beat the campaign without a single death. To be fair though, L4D has an appeal to the non-FPS'er and has no tutorial mode, so a laughably easy mode is probably a good decision on Valve's part.