I spotted this at work when I got back from lunch on Thursday. I couldn't make out exactly what it was, but from the distance it sort of looked like someone wearing sunglasses and a suit and tie looking out the window. I took a photo in hopes of blowing it up and putting the question to rest, but alas, that didn't provide an answer. It was gone completely when I left work, so whatever it was moved or had been moved—as was the sheet draped over the window.
I'm going to write it off as a glitch in the Matrix.