I even hate to say this, but when you guys were pointing out the M in the back seat...what I was seeing in the lower corner directly behind the driver's seat was a face with a hand covering it partly. What you were saying (I think it is what you were referring to anyway) looks like the shadows between the fingers. I agree the rest of the window does show a reflection of the ATM machine/box.
I still can't resolve that lower corner, but if there's a guy in the passsenger back, he's there for a reason since he sticks out (who has the moron driving as a chauffeur?). Probably someone in the driver's back as well.
c6