Forum:MP5K HELP

Hello, I have a question. I got all challenges with MP5K (I have everywhere 100% ) I saw a golden callsign(with skulls on the left and the right side) + embleme for MP5K but i didn't get it?! I don't know what I've forgotten? Is there another challenge I have to do? ( I'm lvl. 50 )

I hope someone knows...

Greetz KaDDisch