upside down and backwards
A hallway at the San Francisco Tennis Club has a bunch of early photographs of San Francisco, including this one (snapped with my iPhone; apologies for the perspective and quality) of the west side of The Embarcadero in 1913.
What I love about this photo (and it's probably hard to see here) is the billboard for Owl Cigars, with the reversed mirror image type. When you quickly walk by the photo of the billboard you do a double take, and I spent a few minutes confirming that this wasn't some weird artifact of the photo itself. (The photo didn't appear to be doctored at all.) The effect of this as a massive billboard must have been something. I'm no student of outdoor advertising, but while I can definitely remember plenty of instances of seeing trompe-l'oeil effects in billboards, I don't think I've seen something as "simply stunning" in a long time.
My colleague Sean Williford pointed out that The Standard Hotels does something related with their logo, turning their simple typeface upside down.
I love both of these -- simple twists that force the casual observer to stop, spend a bit more time processing what they're seeing and become memorable because of their simplicity. That said, if everyone started flipping their type around, everyday life would be more than a bit annoying.
Who else has done this kind of thing well?