Hallmark NK 14 585 ?

Hallo! I have an inherited antique ladies' wristwatch in platinum set with brilliants. The word 'platinum' appears engraved on the inside of the (tiny) case but there are no hallmarks, merely the number 5206 on the case back. No maker's name on the movement, just 'M.P.G' on the barrel.

The strap, however, appears to be white gold, judging by the '14 585' hallmark. What intrigues me are the letters 'N K' within the outline of an open book (rectangle with the corners higher than the middle). Any idea to whom this refers (presumably the maker)? Thanks in advance!
Lucian Comoy