Good question. Although I cannot provide an answer, I can say that I have seen this emblem about 4 times on 4 different people. All of them were level 40 and above. I'm not saying that it cant be a coincidence but I made note of it.
If it is the one called joint ops, then it's an unlock and i believe you receive it after like 5 top 3 finishes in team deathmatch or 10 top 3 finishes. Im no where near 40, so its possible to unlock because i have it.
- Different user**** Im a level 63 and still dont have this emblem. Looked all over the internet for the answer and still cant figure it out
- new user: i have it and i am 3rd level 45. you can get it by setting of a chain reaction of explosives to kill an enemy. hope it helped :)