The police in Germany falls under the authority of the states and not the federal government. Some of them, like Berlin, do require individual number tags.
Additionally you have a constitutional right to fight a government that violates the constitution by any means once legal avenues are exhausted.
And once you file a complaint against the cops for violence, you end up targeted. Either for harrassment (as happened to me) or for frivolous counter-suits ("Widerstand",happened to a couple of friends).
And even if a state like Berlin requires numbered cops, if there are supporting units from other states these do NOT have to carry numbers. Witnessed this first hand when beaten up in Berlin by cops from Dresden.
Additionally you have a constitutional right to fight a government that violates the constitution by any means once legal avenues are exhausted.