"they serve me as the embroidered sign on Siegfried's cloak served Hagen"

   In the Germanic legend of the Nibelungenlied, the heroic Siegfried is rendered invulnerable by bathing in dragon's blood, save for a spot on his back which happened to be covered by a leaf.  His wife Kriemhild is tricked into revealing this weakness (and marking the exact spot with a cross) by the treacherous warrior Hagen, who dishonourably murders the unsuspecting Siegfried during a hunt. 

 

Online edition of the 'Nibelungenlied', as translated by Daniel Bussier Shumway, (originated circa-1200 AD)

 

The Death of Siegfried from Richard Wagner's Götterdämmerung