I just played a match of Nuketown and purposely messed around. I finished at round 10 with 5 downs and no more than 100 kills.

Before the match, I was a normal skull with 4 tally marks. Afterwards, I became the skull and blue eyes with 5 tallies. We already know that lue eyes is not another emblem, but just an indication saying you have 5 tallies.
My kill/down ration is not too impressive. About 33,000 kills and about 935 downs. That gives me a ratio of about 35.7.

Just more information on the ranking system. Goes to show that it may not be exactly what we think it is, and it may be something completely different.