It's almost as though that dialogue is supposed to be referencing either you having the brand, or you seeing the brand on others - but the game does not make this clear and seems to assume it in all cases even where there's no justification for it.
You're right; it's poorly done right now, and doesn't make a lot of sense.
What it seems to be is that you can identify people marked as sworn to the absolute, (but not marked as true souls... but yes with the brand? I don't know, it's unclear), and you, having a tadpole, can use its power to force your willpower on them and have them obey. You can only do this when your tadpole is well rested and feeling peppy.
None of this is explained though - we don't know what symbol its' talking about, we don't know who has it or what we're supposed to be seeing, or where.