The Mark of the Guard is a special mark given to members of the Lion Guard. It is in the shape of a roaring lion's head. Each member's mark changes its color to match their own pelt. It is given to them by the leader placing their paw over their left shoulder.
It seems to be well known as a representation, that the animal that it is bestowed upon, is a member of the Guard. It also function and represent proof in being official members of the Lion Guard.
Those who carry the Mark of the Guard have a duty to defend the Pride Lands.
In trying to figure out how to defeat Scar, Kion and his guard travel deep into the lair to discover the secret to defeating great evil is them. From which a painting shows Askari and his guard coming together to form the Mark of the Guard.
In a flashback when Scar used The Roar to destroy his Lion Guard his mark disappears indicating his loss of The Roar and his title as leader of the guard.
During the final battle against Scar, Bunga nearly almost falls into the lava to save Kion from Ushari. Ono manages to save the honey badger but at the cost of losing his sight. Realizing he's not the Keenest of Sight anymore he passes his title to Anga with Kion agreeing he bestows the mark of the guard on her. With that Ono's mark disappears and becomes disappointed that he's not apart of the guard, however, even though Kion agrees that the egret isn't the Keenest of Sight anymore. He gives him a new title because of Ono's knowledge he is now the Smartest regaining his mark.
Kion and his friends return to see that Kovu and Vitani join Simba's Pride. And while they were gone Vitani led her own Lion Guard in their absence and to prove which Lion Guard is best the leaders agreed to a contest with it ending in a tie. For the final challenge Vitani proposes that both leaders fight, realizing that she was fierce without the roar, Kion surrenders the challenge willingly as Vitani proved herself worthy of the roar. In doing so, Kion passes his title to Vitani with her as the leader of the Lion Guard placing the mark on her shoulder. With that, Kion and his guards' marks all disappear and yet with the roar still needed at the Tree of Life they are given new marks as members of the Night Pride.
An early version of the mark was a lion paw print, seen on early media on books.
There are many mistakes regarding the Mark of the Guard in both The Lion Guard: Return of the Roar and the TV series. The Mark may be on the wrong shoulder, facing the wrong direction, missing entirely, be present in multiple places on one character, or, in the case of Fuli, be replaced with or overlapping with another marking.