The secret revealed

I asked “What do these stamps have in common?”

The answer is: each one of them lacks the conventional orientation of North at the top, South at the bottom, like over 90% of all map stamps. The first two have a tilted compass rose, the last two have the lines of latitude and longitude showing the orientation, and for the one in the middle, you either need to look at a map on your own or you have to be familiar with Bavaria.

Perhaps I was being a bit too devious. What do you think?