(1) According to official ordnance documentation, NM parts (and presumably triggers and sears) were selected from service rifle parts by gauging to tighter tolerances. In most cases, they were not manufactured differently.
(2) NM triggers and sears were polished. But, so were service rifle triggers and sears. NM triggers and sears, however, had to pass tighter trigger pull limitations.
(3) Sear markings vary, depending on year of manufacture.
(4) Triggers were given a blue/black finish.
Hope this helps.
J.B.