Although you can't see it well in the picture I linked to (which I did not take), it does say "Microsoft" in the upper lefthand corner of the building. Which is quite clear from I-405. Also, when I drove by on New Year's Eve, the lights that spell out bing were green, as opposed to the normal whiteish yellow in the rest of the windows. It was immediately obvious to me that they were spelling bing with window lights.