Hitchhiker’s friend Certificate
The certificate contains "Thank you" in many languages and a link to hitchwiki to allow interested people to get more information about hitchhiking. The certificate is subscribed with the hitchhiker's name and optionally further contact details if you want to keep in touch with extremly nice people you meet on the road.
The certificate can be downloaded at the Abgefahren e.V. website. Print it out and give it to your driver, other hitchhikers or people who helped you out on the road. They will like it.