If you travel to NRW, you will get the special forces police units using those kinds of guns on train stations, specially in days where critical football matches are taking place.
North Rhine-Westphalia? (Don't live in Germany, took me a while.)
The other three-letter candidate (Mecklenburg-Vorpommern) is more commonly just shortened to Mecklenburg which isn't an option for NRW because the non-Westphalia part is the more important by far but "north-Rhine" wouldn't really work as a standalone name.
Acronyms for our various Saxonies would be rather awkward because both prefix-Saxonies would collide prominently with an acronym already taken by nazism.
Incidentally when GP said the police "use" the guns at train stations, what they meant was "carry". The German "einsetzen" is more ambiguous about whether something is part of the loadout or actively used (I guess "deploy" is the closest equivalent). I'm fairly certain the guns aren't actually loaded (they're just too big to holster) but at times the Bundespolizei (the federal police responsible for train stations and ports of travel) will indeed carry H&K machine pistols.
Negligent discharges happen every now and then. Usually only injuring other cops.