Marks of the Old Ones

Deep in the jungles of central Lustria are to be found a series of vast geometric symbols carved deep into the ground, each describing the stylised form of a creature of the jungle. From the ground, the Marks of the Old Ones appear as perfectly engineered earthworks, but their true form is said only to be visible to the eyes of the gods. No mortal who walks upon the surface of the world could ever perceive the patterns, and some say they are intended only to be seen by the enigmatic Old Ones themselves.

Source
pg. 34
 * Warhammer Armies: Lizardmen (7th Edition)