The white mark on the tree is called a "blaze". These mark trails, and are usually seen every 1/4 mile or less. If you ever do not see a blaze within 1/4 mile, TURN AROUND and re-aquire the trail. Don't get lost in the wilderness. Blazes can be blue, yellow, red, and other colors. This is one on the 2200 mile long Appalachian Trail.