on pc I have a regular skull with shield no glowing eyes 3 tallys
today was my 2nd day of playing zombies.
Kills: 2736
Bullets Fired:13871
K/
136.8
Downs: 38
Deaths: 20
Revives:19
Accuracy: .68
Headshots: 989
Doors: 25
Perks: 24
Grenade Kills:95
Traveled Miles: 31
But i already am pretty sure its rounds total from all games to rank up.
Then it slowly decreases your rank because you havent been getting enough rounds total to keep it on a certain rank.
On ps3, i had cross bones for a long time, on pc i did about 9 games that all went to about round 15-20 each.
I noticed my rank increase in my last game i played (solo town) after round 21 i died, and i hit Tab, and saw it had gone up.
On ps3 i did the round skipping glitch and went from crossbones to shotty in 1 game. I cant see it being k/d because when people are noobs they destroy it and could never rank up.
I think it is most likely a ratio of kills/rounds achieved.
In a little while i will post my stats on ps3 since i had shotgun ranks (might have lost it)