I believe the "PS" in the shield stamp was on a run of "Police Special" 92's that were produced for LE. They came in a cardboard box with the same mark instead of a hard case since duty guns usually stay on a shelf in a locker or in the duty holster... they rarely get stored in a case by LEO's... at least in my experience. My Glock 22's case has sat at the bottom of my locker since day one, lol.
Pretty sure they are the same as other 92's (no special features like "G" models)... they were just intended for LE sales. Some were most likely available to civilians or dealer specials. The finish should be more of a matte finish vs the more glossy (Bruniton) finish on other models. Sold with 3 mags as well instead of 2.
I have a 1993 "PS" (Police Special) with the "PS" stamped on the slide inside a badge emblem and "P" stamped on the trigger guard inside a badge emblem. It's a "92G" model with the 92G stamped on the slide. The pistol has a smooth dark blue finish. When you de-cock the pistol if the de-cocker springs back up it's a 92G if it stays down on safety it's a 92FS. It may have come with Trijicon night sights as well as did mine.