The name Siegfried is not based on the character Sigurd, rather both names are variants of the same character from old Germanic legend that split during the migrational period around the 5th century from ancient Germany and became heroes of two seperate societies of the same origins in the heart of Europe/Germany (or by roman terms Germania). Therefore both characters are of ancient German decent and were not recorded until after they split in the 1200's much like the homeric poems such as the Iliad and Odyssey were passed down until an unknown finally recorded them. It is for this reason that there is a large bias in both versions of Siegfried/Sigurds legend the Niebelungenlied and the Volsungasaga such as the Niebelungenlied's tendancy toward medieval society even though the myth is ancient. Interestingly enough also there is speculation on the relations between Arminius and Siegfried/Sigurd in that he may be the real life inspiration to the legend or at the very least a strong contributor to the myth by rising to the occasion as a hero based on the stong ties and evidence between them.
This is the name of James Herriot's employer in his books about his life as a country vet (Most notably, All Creatures Great and Small). When questioned about its origins, Siegfried explained that his father was a great fan of Wagner.