The mark of grace is a token that was released 5th December 2013 and can be obtained on a semi-random basis by using the Rooftop Agility Courses. The tokens appear at specific locations on the ground during the course of a lap in varying degrees of frequency. Also, multiple marks of grace can spawn. The likelihood of obtaining a mark of grace varies based on the difficulty of the course, with higher level courses having a greater chance of spawning them.
A player's agility level does affect the chances of one appearing. Chances of receiving marks of grace decrease when your agility level is higher than the requirement of the agility course.