Check if a Sprite is part of an Atlas or not?

I'm trying to determine if a Sprite is part of an Atlas or on it's own. It's to alert people in a custom inspector if they're trying to tile a sprite from an atlas, or not (we don't want to tile from an atlas).

Is there any command I'm missing to determine from the Sprite itself if it's a member of an Atlas or not? Sprite.packed doesn't seem to do it unfortunately, and I can't find any other reference.