Lichens are complex and fascinating and take time to get to know. Once befriended they can be used to help you navigate naturally.
On stones, whether in the wilderness or in a town, it is common to find mosses on the northern side and golden coloured lichens on the southern side. There are few rules that can be applied across the board to lichens, this is part of the satisfaction of building up local knowledge, but one that has worked for me is as follows: if a lichen has a golden appearance then it is more likely to be on the southern side than any other. A good way to remember this is by thinking of it sharing the gold of the sun.