This will likely come before any other Triad or Face Level achievement. Especially if you have the Top Dog Silver Pack DLC, which gives an automatic 5 level boost to your levels. In order to level the Cop rank, during missions you will have to ensure that you do not kill innocent people, cause property damage, steal cars, etc. The more you do the aforementioned things, the more points the game will take away from the Cop experience you will earn after a mission is completed. You will automatically begin missions with a 3 Cop badge rating, and it will gradually go down over time if you steal, kill innocents, etc.