A clue: Look for big important buildings you might know.
Yes, that's right. I was in Berlin (again).
When I realised this, I thought how great. Let's use the semiotically most important symbols of our city to decorate the way you get around them.
I know that the Tube has a different pattern for the seat covers for different lines as witnessed by another quiz here but that's making it too difficult for tourists.
Imagine fitting the symbols to the places the line goes under or even to. You could have Buckingham Palace on the Piccadilly Line and the Victoria Line because they both go to Green Park and it would be a much nicer of way of working out the intersections.