Who is the sign for? If it’s for hikers of the trail, they will know which direction to go, but nothing more. If it’s for tourists visiting Harpers Ferry, they will know that Maine and Georgia are almost equidistant from that point, and opposite from one another. I know that the trail extends from Maine to Georgia, but I saw folks looking at the sign yesterday who definitely did not.
How much can signage assume? Public signage in a place where anyone can go probably can’t assume much. In libraries, we make signs with the guiding principles “clutter is bad,” and “information is good.” To make a better sign, ask yourself, “who will see this sign,” and “if they had never seen this sign before, would they know what to do?” No detail is too obvious to consider including.