I have borrowed this photo from Jan's Gun Boards site...
I thought I read somewhere in John Walter's book that the "c" on presentation pieces was used only on carbine models. If this is true, it does not appear correct on a Navy piece...???
Text Added by Pete : "The Luger Story" by John Walter, page 102, last 2 paragraphs along the page. I might be wrong, here...but didn't the German's spell carbine with a "k"...???