This is a small supplement to my previous question about the jinmeiyō kanji. Are they also used regularly in place names, like cities and towns, or only for people? And are place names similarly difficult to guess the pronunciation of without asking? Are furigana typically used on signs and documents for place names?
Place names, and surnames use whatever kanji they're supposed to, however unusual they are. Japanese kanji policy has no regulation for existing proper names (though they do for given names of newborns). The preface of 常用漢字表 has a line:
This chart does not affect proper names except kanji used in prefecture names and their equivalents.
That's why Japanese government maintains a huge number of variants for resident registration.
Of course the same applies to reading. For some reason, English WP has a list for Japanese unreadable place names whose great portion is unimaginable without pronunciation aid except for local residents.
Thus, documents targeting locals isn't likely to put furigana on them, but those expect public to read, such as newspapers, may well have furigana. I have never seen road signs have furigana though, probably because they always have romaji instead.
All reasonably sized JR stations (and AFAIK, all JR East stations) and many private railway (non-JR) stations have Furigana on their 駅名標｛えきめいひょう｝, or station name signs. For example, this is the sign for Tokyo Station in Chiyoda, Tokyo: . Source: Wikipedia (public domain image).
There isn't a big need for furigana on road signs, though. Not only because the road signs can't really fit them, but also because road signs have Romaji, which pretty much everyone could read. There indeed are a lot of surprises in toponyms, such as 不忍｛しのばず｝, but even if one is new to Tokyo (where Shinobazu is in), he/she could know the pronunciation from the Romaji.
Regarding kanji usage - not only jinmeiyō kanji are common, rare kanji in neither the jōyō nor the jinmeiyō tables are not a rare scene as well. For example, in Tokyo Metropolis 東京都, there is a city called 狛江｛こまえ｝市, where 狛 is an example of a kanji that's neither jōyō nor jinmeiyō.