One thing rings a faint bell with this, but very faint: there was a make of frame that we usually saw coming from Benelux and some were CX frames but marked with a single "D" engraved in the lugs and maybe also forkcrown. And IIRC the font was very similar to this "C" but I don't think there was ever any brazed-on head ornament. IIRC (again) there finally was an ID made for this mystery make and IIRC (3rd time) it was some connection to Martens/Martelly. Maybe there's some "Benelux trail" to follow with this one...just a thought.