The October (5/06) issue of Spielbox magazine included a mini expansion for Thurn and Taxis, Der Kurier der Fürstin or The Princess's Courier.

Certificates of Nobility: Setup - players add certificates of nobility to every city on the board. When a postal house is built in a city for the first time, that player gets the certificate. Two certificates may be spent to obtain the powers of the additional officials on a player's turn. 

The Princess's Courier: If a player scores a route and receives no carriages (or declines to take one), they then receive the courier token. If a player has this token at the start of their turn, they only need to spend ONE certificate of nobility to gain the power of additional officials on their turn. The courier token is worth one point at the end of the game.

This mini expansion is language independent, but the rules were available only in the Spielbox magazine and only in German. An English translation of the rules can be found HERE (thank you to BGG user Minok). This listing is for the punchboard only and NOT the Spielbox magazine.

For more information, please refer to the BGG listing.