The Zentral- und Landesbibliothek Berlin (Central and State Library of Berlin) put’s the “Berliner Bär” (berlin bear), which is the heraldic animal of the city, in the middle of their stamp. It has a very nice shape.
The only problem: The light grey color makes it sometimes hard to find the stamp inbetween the data on a crammed page.
The Zentralbibliothek holds the right to the deposit copies (“Pflichtexemplarrecht”) for the state of Berlin. It puts those copies also into the normal stacks, but uses another stamp for them – this one.