[buster]

To be clear, not every entrance has exactly this. It's probably always a white square with a black number, but the font can be different, etc.

I looked it up. Of course we have a law for that: https://gesetze.berlin.de/bsbe/document/jlr-GrNrVBEV3P4

The sign has to be visible at night, coming from both directions and needs to be at least 10cm large... That's basically it.

[rob74]

That's interesting... actually the directive only specifies that the numbers should have sufficient contrast against the background, be at least 10 cm large and have their own light source. So, while most seem to have settled on "black numbers on a white square", you are actually allowed to do something fancier if you want. Other cities (like Munich, which I mentioned in a sibling comment https://stadt.muenchen.de/rathaus/stadtrecht/vorschrift/310....) have more strict design rules, but don't require illuminated numbers.

[ttrrooppeerr]

Thank you! It was a small itch I had while walking around the city and you managed to scratch it, really appreciated.