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.

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.

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

Not sure about Berlin specifically, but many (most?) larger German cities have rules about how the house numbers should look like - after all, Germans love rules and regulations! And this is actually helpful, as it's much easier to find the house number on a house if they have a consistent look.

IMHO the Munich house numbers are better than the Berlin ones, as they also include the street name and (most of the time) an arrow pointing out the numbering direction (https://commons.wikimedia.org/wiki/Category:House_numbers_in...). Not sure what that font is called either though...

> many (most?) larger German cities

I guess those qualifiers cancel each other out? Anyway. Berlin is twice as big as the second biggest city, Hamburg. Munich is the third largest city:

https://worldpopulationreview.com/countries/cities/germany

We've gone over Berlin and Munich, here's Hamburg:

https://www.hamburg.de/contentblob/153026/31a1e4447ce01eb4b8...

- must be placed at least 180 cm above ground, near the entrance or on the side facing a public road

- if the building is too far away from a public road for the number to be recognizable, it must be placed at the entrance of the premises, no lower than 90 cm above ground

- it must be made out of a material that can withstand weathering and provides good visibility of its shape and color

- for certain buildings (office buildings?) the numbers must be illuminated to be visible in low light conditions

Here's #4 on the list, Cologne:

https://www.stadt-koeln.de/service/produkte/00930/index.html

- it must use "arabic numerals" (i.e. not Roman numerals) which must be at least 8.5cm high

- it must be visible and legible from a public road

Frankfurt am Main (#5) does not seem to specify any requirements and thus defers to Hesse, which doesn't seem to specify any requirements either.

https://frankfurt.de/themen/planen-bauen-und-wohnen/planen/s...

I'm not going to go over the rest of the list as the lesson seems clear: some cities/municipalities have strict regulations, some barely have any, size doesn't really seem to be a deciding factor.

It is the Hausnummer (building number). Every building has one and the signs have to fulfill certain requirements.

Usually they increase from the city center outwards, even numbers on the right side, odd numbers on the left.

We write them always after the street name, which drives Google Maps and other badly internalized software nuts.

Buildings don't have official names, some have informal ones, like the Gropius Bau.

Only slightly related but at my house in rural France, at some point the way houses are numbered changed : each house now has a number which is the distance, in meters, from the beginning of the street (and probably with even/odd depending on which side of the street you're on: didn't check).

But, without asking, the authorities did install the new numbers plate on every single house. So it's all consistent, everywhere.

The official reason is if an ambulance or police car has to find a house: because previously none made sense it was hard to find (it's very sparsely populated). Now the idea is that the driver can just engage in the street and drive x meters and he'll be in front of the correct house.

I take it in Berlin there's t least something a bit related in that they have to be visible in case of an emergency (but I'm just guessing).