The C/N proof is a "Nitro" proof applied to a commercial Luger when it's passed firing the proof load.
A Navy Luger should have C/M markings. You'll find several pictures of actual Navy Lugers on this site.
Was it in 9mm Luger or .30 Luger caliber?
It's most likely that it was a DWM commercial. Those are often the donor for a faked Navy Luger.
Hard to be specific without pictures, which you likely don't have... Oh well. Check out the real ones posted on this site and let us know from your memory how close his Luger was...
Pictures of the real thing were just posted over on Jan Still's site:
http://luger.gunboards.com/showthread.php?t=27973
Marc
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.