Making the German state officially state that this is Nazi imagery would be a worthwhile win lol.

There's plenty of "fair use" cases which would allow it.

§86a STGB allows for the use of "symbols of anti-constitutional organizations" in cases of:

• art (e.g. the movie "Downfall")
• scientific research
• education
• news or other broadcast (covering Nazi Protests in the US for example, German news station don't have to censor the Swastika flags or the like)

And probably applying in this case - in protesting said anti-constitutional organizations, for example a crossed out Swastika as a form of protest against Nazis is still very much legal.

Most important is the intent. If you plan to use those symbols with the intent of furthering the ideology of anti-constitutional organizations, it is probably forbidden. The intention has to be clearly against those organizations, otherwise it might be actionable.

Btw the communist party of Germany, the KPD is also considered an anti-constitutional organization and therefore it's symbols are forbidden in the same way.

It is with few exceptions. Given that it looks like the purpose is to call out a Nazi supporter I think they wouldn't get in trouble for that though.