How certain are they?

When I saw this, I read it as an ingenious and funny reference to Heisenberg's Uncertainty Principle. But now I'm told it's just a reference to a TV show. (It might still be ingenious and funny, but I don't watch much TV, so I don't know. It might not.)

"Heisenberg - Live free or die"

More postcards follow.

My other favourite was the message on the back of a kiosk selling magazines, sweets, mobile phone credit, and whatnot. I didn't take a photograph because my internal risk manager declined to get the camera out, but it read:

"ICH BIN LADEN"

Which is German, and means:

"I'M A SHOP".