The "Badge" is essentially resembling a pirate flag (white skull with crossed bones on black background).

Hamburg, of which St. Pauli is a nation-wide well-known area often in the media because it's red light district and its most known police station, is also traditionally a hot spot of militant antifa scene.

In 2017 the antifa turned that city into a burning hell looking like civil war area.

If that would not be enough, there is a building squatted since 1989 by far left scene.

So, it is not that counter-intuitive to associate fans of Germany's most violent soccer club with the far left scene of that city...