I run pugs alot and have seen people of all types and (almost) have never seen people using Dragonmarks, I do know that there's an option to "hide" that blue stuff on your character's face, but I only have seen one or 3 Chestbuffers (Dragonmark of Finding) in the past 5 years I've played this game.
What am really asking is just how "exactly" useful do Dragonmarks play in this game?