In the opening titles of each episode, the letters on the Fawlty Towers sign began to go missing and then in later episodes rearranged into partial anagrams of Fawlty Towers. Almost every other Fawlty Towers website has them, so here they are…
Episode One: A Touch of Class. The "S" hanging down
Episode Two: The Builders. The "L" hanging down, "S" missing
Episode Three: The Wedding Party. The "L" and "S" both missing, the "W" of Towers hanging down
Episode Four: The Hotel Inspectors. The "L" and "S" are both missing, as is the "W" of Towers. Like Basil's sanity, the sign is disappearing with each episode. The "Y" of Fawlty is now looking ready to drop.
Episode Five: Gourmet Night. The gradually disappearing letters has now been abandoned in favour of a partial anagram of Fawlty Towers: for this episode "Warty Towels"! I think it would have made a good ongoing funny scene if Basil, at the start of each episode, handed Manuel the letters which had fallen off and told him to go and put them back on again. You would then see Manuel standing in front of the sign looking perplexed before sticking the letters back on to make the anagrams, but thinking he has done it correctly.
Episode Six: The Germans. The Germans was the only episode that didn't show the exterior of Fawlty Towers in the opening credits; instead it showed the outside of the hospital that Sybil was in for her operation.
For Fawlty Towers trivia buffs, the hospital used was Northwick Park Hospital in Watford Road, Harrow, Middlesex. Nowhere near Torquay — most of the exterior locations were in the North London area.