It doesn't have to be historic interest actually, it just means national heritage or place of interest (sign H22).

More like, a place "worth seeing".

FTA: “Finally she came across a floral symbol that was used in Sweden to indicate an interesting feature or attraction in a campground”

⇒ the article likely is wrong by adding “in a campground”, but it doesn’t say it means campground; it’s ‘only’ its title that does so.