All those people wondering about / looking for the "real" origin of the Ku mark; it's a bit like looking for the "Holy Grail" I think, so far I've heard about few (5 or 6 at least) different theories about the origin of that mark, one of which is explained in the below link.
Who knows, unless some written documents will be fund, unfortunately the few people that probably worked at those scarce Lugers are not alive to let us know the truth any more.
Anyway so far I've never seen a "Ku" Luger. :-(
Sergio
http://www.icollector.com/Unique-Wor...-and_i15827729