Give 250 Tourmalines to Losanil in Lowangen, in A Run-Down Courthouse (15909) off of Dargon Walk.
Answer her question with "offensive" to receive the Mark of Assault.
Answer her question with "defensive" to receive the Mark of Barrier.
Note: This mark gives no rewards, but it will enable you to wear certain pieces of equipment. Check out the Barrier Gear List for examples.