Possibly referring to NK as a brand? There's no major camera maker called "NK," but Nikon is sometimes abbreviated as "Nikon" (N.K. could be initials of a person reviewing a custom camera).
These cameras were rarely original designs. They were often precise reverse-engineered copies of the Leica III (styled as the "Kumgang-San") or the Japanese Miranda. The irony was palpable: while the state preached fierce anti-imperialism and self-reliance, their prized consumer exports were meticulous clones of Western and Japanese technology. nk camera
"NK" could stand for "Not Known" (unrecognized camera brand or model) or in some online marketplaces, "Nice Kit" 鈥� though that's a stretch. Possibly referring to NK as a brand