As Grover Whalen said, there is plenty of law at the end of a nightstick. Police in Germany – as in most other countries – has the monopoly of the use of force. Difference to other countries: In Germany the Police is to a large extend and due to federalism a matter of the Federal States (Bundesländer). That’s why police uniforms look differently from region to region.
Alongside the ordinary police forces in Germany a trend can be observed to more and more uniformed municipal police which is part of the so called „Ordnungsamt“ (Public Order) wich is in turn part of the local administration. Their introduction was a reaction from cities and municipalities of (supposed) increasing safety problems in urban environments, like open drug scenes, a trend towards neglect or just a lack of cleanliness.
I can’t judge if the development of increasing municipal police forces is a necessary one, but I am concerned about the lack of clarity in public regarding the rights of this local police forces.
Unlike their public appearance of being a sort of police (they often adapt the style of uniforms and equipment from the ordinary police forces, example from Frankfurt am Main), their rights are restricted and depend on the local administration.
So the rights differ from town to town plus there are different rights ordinary police forces have compared to municipal police forces. Therefore there is a lot of room for confusion which is a bad initial situation to ensure safety in public space.
In modification to the quote of Grover Whalen: In a country under the rule of law one has to know who has the right to use a nightstick – and how hard is he allowed to strike.