It has the obvious kick up in the rear door, reminiscent of the SM, but has anyone noticed the door top line?
Every-time I see this line it makes me think of the roofline of a DS, as it rolls over from the door, rises slightly in an arch then tapers to nothing at the trail edge.
It's hard to describe, but once you know it's there, you can't miss seeing it.

I watched a film called "The Whistleblower" last night. At one point the main character was waiting in a car in the dark. There was only a few seconds of this scene and all it showed was her through the window, but as the camera panned it showed the window breaks and this roofline. I knew it was an XM she was sitting in.