These Marks can be turned in for items. You need to faction (Orcish Dissention Quest) to be able to talk to the NPC (Fergarin Bardon I) that you turn them in to. Hope this helps :))
I've heard rumors of it being for faction. So far all just rumors.
I've tried turning in one to Wraithguard Heimgul in Valdeholm. He says "You must turn in all quest pieces at once to complete this quest" I've tried turning in two, three or four at a time, all to no avil. This quest involes other components but I'm not sure what. Maybe the shadow forged weapons and slivers of dark essence and something else I've not seen yet?
I've been trying to find info on - crystal of daylight - some stuff I read said it was from a vald faction task too.
Hard to get guild interest in the factions out here yet when we are still farming demi:(