Earlier quoted context omitted.
In many countries fire hydrants are underground, under an iron or concrete cover. There's very little to see on the street. There might or might not be a sign marking the location. Sweden: https://commons.wikimedia.org/wiki/Category:Fire_hydrants_in... UK: https://commons.wikimedia.org/wiki/Category:Fire_hydrants_in... It's also not necessarily relevant to worry about blocking one when parking a car.
Most UK hydrants are at junctions where its already illegal to park... come to think of it, I think USA ones are maybe mostly at junctions (in the media I've seen)? Are you allowed to park at junctions in USA?
US driving laws vary quite widely depending on the state (and sometimes depending on the city within the state). So there’s probably no uniform answer. But parking at an intersection is indeed allowed in a lot of places within the US, in my experience.