Would the duration last on the person who is marked? Because if it lasts on the assassin then they can still log out until the timer is gone and then come back. If it IS on the person who gets marked then there should be an echo saying something like "You've failed to kill your mark" or something like that.

But also with a duration I think there should be a little more utility to mark of the prey. Maybe nothing HUGE. Something like actually being able to see your mark on "where" when you're blind or being able to locate your mark across different continents, for a larger price of course. (can you already do this?)