Bayreuth, not Berlin (but who cares about spelling of German towns) and 'park' not 'parks'. One single park in Bayreuth is where this happens.

I can be wrong, but the most likely interpretation is that this is a protest not against the USA but against dog poop (and bags with mixed party flags are more expensive than those with just a single flag). Dog poop in a local park, that's what really angers a typical Bavarian and could lead to a revolution, but foreign politics who cares about that?

Wolfgang