Apparently the Passau Wolf goes back to a guild coat of arms granted by Emperor Charles IV in the 14th Century:
“In Germany, as far back as the thirteenth century, the cities of Passau and Solingen were famous for the production of sword blades, and early in the fourteenth century a celebrated armourer of Passau named Springenklee received from the Emperor Charles IV. a coat of arms bearing two crossed swords to be used by his township. The mark of the wolf, or running fox, as it is sometimes called, which is commonly associated with Solingen blades, was common to those of Passau as well, especially in the thirteenth century; it is supposed to have been granted to the Armourers’ Guild of Passau by the Archduke Albrecht in 1349. Until the custom was suppressed by the French, Solingen had a stamp office in its large market place, where the smiths were obliged to bring their work to have it proved and stamped.”