Linguistics

We use it in Denmark on signpost for directions to local attractions

No idea about @ but it seems to me that people have been circling letters as part of a personal signature (like if your party name started with an A, you might just sign and circle A) for a long time, but I’m not sure it’s the right answer.

The article explains it, but the origin is from Latin ⟨ad⟩ for, toward, at in the Middle Ages. Faster to write, less paper and ink necessary (those can be expensive).

There's a bunch other symbols and diacritics that popped up back then, for roughly the same reasons. From what I recall:

• ⟨&⟩ aka ampersand — from Latin ⟨et⟩ "and"
• ⟨º⟩, ⟨ª⟩ aka ordinal indicators — to disambiguate ordinals and cardinals while using Roman numerals; e.g. in Old Italian ⟨X⟩ would stand for ⟨diece⟩* "ten", ⟨Xª⟩ for ⟨decima⟩ tenth, F and ⟨Xº⟩ for ⟨decimo⟩ tenth, M.
• ⟨~⟩ aka tilde — from a superimposed ⟨n⟩. In Galician and Portuguese it was often used because some scriber forgot to plop an ⟨n⟩, since the /n/ was elided from speech; e.g. Latin ⟨pinum⟩ → ⟨pino⟩ → ⟨pĩo⟩* "pine". Then in Spanish for old ⟨nn⟩→⟨ñ⟩, that was sounding less and less like /n:/ and more like a single sound, /ɲ/.

*old spellings. Modern ⟨dieci⟩ and ⟨piño⟩ / ⟨pinho⟩ respectively.

No idea about @ but it seems to me that people have been circling letters as part of a personal signature (like if your party name started with an A, you might just sign and circle A) for a long time, but I’m not sure it’s the right answer.

I was also surprised when I saw ⌘ on a sign in Finland. It has a longer history than that, even.

I’m pretty sure it is just the Cool S with Finnish characteristics