Thats what I thought might be the case. I think your NH may be a jewelry store or merchandisers mark if it a part of or near the gold quality grade mark (such as 14K). Jewelry stores often have their own mark inscribed on their finer jewelry.

Difference between hallmark and trademark:
"

How are they differentiated from hallmarks?

There are some points of distinction between hallmarks and jewelry trademarks. Firstly, trademarks protect the work of the manufacturer who has made the jewelry but a hallmark does not. If any other manufacturer, without the original manufacturer’s prior permission replicates the design of the jewelry, the latter can sue the former in a court of law for infringement of trademark. As such, a trademark gives the maker an exclusive right to claim the design as his, which cannot be copied by anyone else.

Then, trademark only discloses the name of the manufacturer of the jewelry while hallmark contains some other information also. Hallmark discloses the kind of metal used in making the jewelry, the origination and even the name of the artisan in some cases. So basically, a trademark simply protects the right of use of the maker, whereas a hallmark gives other information which is used by the buyer."

ref: http://edu.udym.com/trademarks-for-jewelry/

I would assume that your ring is marked with a hallmark and they are very hard to recognize except in the area of the artist or jewelry store. We do not have a directory of them like we do for trademarks. Enjoy your ring and if I can help you further, let me know. My best, Randi