Disclaimer: I have not yet punned in German. I am far, far away from being capable of that.
I did, however, understand a pun stenciled on a wall in the 6th district:
It means, ‘Women. Free and wild. Not fair game’.
‘Wild’ means ‘wild’, ‘frei’ means ‘free’, but ‘freiwild’ means fair game. Geddit?
A a bonus, here’s another:
It means something like ‘fight against sexism’. No pun, but hey, you gotta love a classic.