Right, so I wrote some more too, "something that isn't ancient in some scientific sense but still is a place of historical or archaeological interest".
An athletic facility that's been going since the late 1800s and has a dedicated museum and is of distinct local cultural importance kind of fits the "historical interest" part pretty neatly.
As your lovdata-link shows, there are six different signs for severdigheter, not just one, and in the local parlance severdighet typically refers to things like historiske steder, monument and so on. Unless something has a bit of history it's unlikely to get one of those signs put up.
By this interpretation pretty much any attraction that isn't brand new is covered, which would entirely dilute your main claim of describing it as referring to ancient monuments or "fornminne". "Fornminne" has a specific meaning and certainly would not generally be applied to a relatively modern place of "historical" interest in Norwegian, nor would it e.g. refer to natural formations.
The other 5 are for narrower, more specific use, and demonstrate quite clearly that the word "severdighet" in Norwegian has nothing specifically to do with historical interest. When you then try to insist that the general, catch-all sign does it feels intentionally obtuse.
To make this clear, here's an example of a sign to INSPIRIA Science Center[1], built in 2011.
https://g.acdn.no/obscura/API/dynamic/r1/ece5/tr_1200_1200_s...
Reading this I assumed the symbol referred to a castle with a turret in each corner
It's older than castles and occurs in some of the oldest scandinavian stone carvings. In the middle ages it was associated with John the baptist in Scandinavian christianity.
The use discussed here is established from the 1950s onwards, first suggested by a local history society in Finland.
