WST DTM/Law Enforcement
From Halopedia, the Halo wiki
The M90A Law Enforcement is a version of the DTM Series used by Law Enforcement agencies. It features a solid stock and no pistol grip. The shotgun would appear very similar to a real-world Remington Model 870 shotgun. The lack of a pistol grip might be a downside in military combat, but allows the user to hold the shotgun with one hand comfortably and direct traffic and so on, making it useful in this way.[1].