25 Pfennig, Braunschweig motor transport company, 1921

Notgeld began in 1914 as necessity: silver and nickel coin vanished into hoards within weeks of mobilisation, and towns printed their own small change because the Reichsbank could not supply enough.

By 1920 it had become something else entirely. The shortage was easing, but the market for the notes was not - collectors would pay well above face value for a complete set, and a town could take real marks for paper it hoped would never come back to be redeemed. So the municipalities commissioned Serienscheine: lithographed series, four or six or ten notes to a set, printed far beyond any local need and illustrated with whatever the place was proud of. Local legends, famous sons, battles, saints, jokes in dialect.

The result is the most inventive body of graphic design in the history of paper money, made by places with a few thousand inhabitants, in the years when Germany's currency was dying.

Not a town but a bus company: the Kraftverkehrsgesellschaft of Braunschweig, a state-and-municipal undertaking running motor coaches into the Harz. The voucher is redeemable at the company's own offices in Braunschweig, Bad Harzburg, Braunlage, Hahnenklee and Wernigerode - a list that is really a route map - and it expires on 1 January 1922.

Both faces put the coach in the mountains. On the front two gnomes watch it cross a bridge; on the back a giant, captioned Der wilde Mann, sits on a hillside above the road while the bus goes by beneath him. The Harz is the German folklore mountain - Walpurgisnacht, the Brocken, the wild man of the woods - and a bus company selling excursion tickets in 1921 knew exactly what it was trading on.