Unable to answer "What diameter is specified on the sign for this fire hydrant?" – 822 (Pillar Fire Hydrant) – https://osm.org/node/11346101975 via StreetComplete 62.1:

Ist kein Schild.

Attached photo(s):
https://streetcomplete.app/p/323842.jpg
https://streetcomplete.app/p/323843.jpg