Upload & Sell: Off
It is an outside corner. The left hand face has rows that stick out. It isn't a strong effect, but I noticed it when I getting ready to post it. It just kind of popped back and forth, so I went for it as a name.
I did rotate the picture 180 so that the shadows fall 'up' instead of down. I thought that helped to keep the brain a bit more in flux since we expect shadows to fall, not rise. Less of an angle on the shot might have made it more difficult to guess the orientation.
Thanks everyone for the comments.