The USA release of Ninja Gaiden Sigma Plus for the PS Vita, specifically with the "NoNpDrm" label, indicated that the game had been patched to remove the DRM protection. This meant that players could enjoy the game without any online requirements, making it a more appealing option for those who preferred to play offline.
Inside that folder, you find:
He ejected the SD2Vita and held the cartridge in his palm. This wasn't just a pirate's booty. It was a time capsule. The US PSN store for the Vita was on life support. In a few years, when Sony inevitably pulled the plug entirely, there would be no legitimate way to download this version of the game. Physical cartridges of Ninja Gaiden Sigma Plus were rare and cost a fortune. But this? This file would outlive the servers. Ninja Gaiden Sigma Plus PS VITA -USA- -NoNpDrm-
to bypass DRM, allowing it to run on modified Vita consoles. Core Technical Specifications Developer/Publisher : Team Ninja / Tecmo Koei. The USA release of Ninja Gaiden Sigma Plus