As a general rule, the Eickhorn trademark with the squirrel holding the sword and the words "original Eickhorn Solingen" should be stamped. On Luftwaffe swords it is usually etched, probably because of the profile of the blade. However, I don't think anyone can say for sure that this is a rule without exceptions. Another rule of thumb is that when the sword blade is pointed down, the trademark should be right side up. Eickhorn usually put the trademark on upside down on post war swords.
Joe S.