Thaaaat'd be easier. Since that... immediately includes demons(though not all demons are evil at all, the Church isn't exactly a fan), liches(well, the most likely type at least), anything Hidroroth-related, mindless undead, and vampires.
Maybe make it visually a magically-generated Fleur de lis? Or sun.
Was thinking a sun made with some of the caster's blood. But either is fine.
Edit: done.