Looking for the answer for at least ten years according to this link:
http://alphabetilately.org/NTS.htmlIf we can take some of the references shown in these previous posts, it has been determined that the stamps were apparently acquired by a railroad enthusiast, so it is fair to reason that the stamps could be connected to a railroad, perhaps intended to be attached to a ticket or transfer of some sort.
Most everyone agrees the first two letters are "NL". The first thing that comes to my mind is New London (as in Connecticut). As there were several early passenger and freight railroads in that area, could it be connected?
Just some thoughts that might move this toward some sort of a resolution.