Beast Marks are bestial features which are left on a Gangrel during Frenzy, due to their clan weakness. Gangrel are deeply attached to their inner Beasts and therefore when they succumb to frenzy, their Beast leaves a taint on their body. This is most of the time marks of animals the Gangrel is affiliated with. Examples include cat-like eyes for a Gangrel which has associations with felines, or webbed fingers or large ears for a vampire who identifies more with bats. The marks are the reflections of the Gangrel's inner Beast.
Conversely, if a Gangrel takes form of a wild cat instead of a wolf by using their Protean Discipline, they are unlikely to take a beastly marking of an aquatic creature during frenzy.