"Wolf-runes were carved into the trees in every direction around the hills; they signified: 'Beware! Before you is an abyss, and should you fall in, you are doomed!'" - Hermann Löns, 'Der Wehrwulf', 1910.
The image below is of the second English translation of the German 1910 "Blut und Boden" peasant revolt classic 'Der Wehrwulf' by Hermann Löns. (Westholme, Yardley). The first being translated by Marion Saunders, New York: Minton, Balch & Co., 1931 and entitled 'Harm Wulf: A Peasant Chronicle.
There's an article about his life and work by Markus Wolff in TYR Vol. 1.
The Wolfsangel on an old field boundary stone in the Deister in Lower Saxony.