What is the N7 that's on Commander Sheppard's logo all about?

What is the N7 that's on Commander Sheppard's logo all about?

N7 represents how far Sheppard has progessed through Interplanetary Combatives Training programme. What it means is that they are the best of the best at being a soldier.

Interplanetary Combatives Training (ICT) is the Systems Alliance's premier school for leadership and combat expertise. The Interplanetary Combatives Academy, is often known as "N-School" or "the villa," recruits officers from every branch of Earth's militaries to partake in grueling courses at Vila Militar in Rio de Janeiro.

The highest grade of training, N6, provides actual combat experience in combat zones throughout the galaxy. If the trainee survives these scenarios in "admirable and effective fashion," he or she finally receives the coveted N7 designation. N7 is the only ICT designation that may be worn on field or dress uniforms so it was sure amusing for Sheppard to find the Geth we know Legion wearing it in Mass Effect 2 - it was kind of an homage to the man.

If you've played through Mass Effect you'll recall that James Vega was asked to go through the ICT program.