You are among few who are born with the ability to see magic in its raw form around the world.
You're able to see without any required checks if someone is a spellcaster, as well as whether or not an individual possesses a soul. However, areas rich with magic (especially Leylines) inflict Blindness at Low Intensity to you for 1d4 rounds the first time you see them in a day.
You must be born with this trait, and it can only be taken at character creation.