This Really Does Happen

I was at an opening reception for an art show the other day and one of the artists walks into the room, looks at the opposite wall, and frowns a frown of tolerant amusement. Then he goes over and takes his painting off the wall and turns it 90 degrees—apparently it had been hung upside down. So I suppose if you're doing abstract stuff and you can't be at the show to check, it might make sense to put one of those "This Side Up" arrows on the back of the painting or something.