Yeah, I was thinking that Alpha, Sigma, and Phi would be the most common letters... Oh hey, Alpha Sigs. :P

1. Eta
2. Omicron

I had to look them up because I'm in a NMGC org so I am not very familiar with NIC and NPC.

Just to quickly reply from the quizmaker since the thread keeps going. The answers are Eta and Omicron. Congrats to all who got them!