N7

From Mass Effect Wiki

'N7' is a vocational code in the Systems Alliance military. The 'N' designates special forces, the 7 refers to the highest level of proficiency. It applies to marines who have graduated from an elite training programme and shown immense skill in the field. Both David Anderson and Commander Shepard are classified as N7; Anderson was one of the first graduates.

If Shepard is equipped with any weight of Onyx Armor, the distinctive N7 and red detail on the right arm will be emblazoned on it.

The Medal of Valor achievement (completing Mass Effect on Insanity difficulty) unlocks an N7 gamer pic.