While I don't know who made most of the carvings, This one, I believe is from a boy who went to school with one of my children. The carving has been there for at least five years and I think it is closer to ten.
I have no idea who SC is. There appear to be dots in the shape of a question mark. I wonder what the question was.
The marks at the bottom of the tree were probably made by someone sitting down, making me think of my father hitch hiking home from somewhere. He and his friend reclined by the side of the road raising their thumb whenever a car passed, not understanding why no cars stopped to pick them up. You don't get far lying down.
This one, I'm pretty sure was done four years ago. Though the tree has healed around it, It is still easy to read. The less detail in a beech carving, the better. It is also important to leave plenty of room between your letters. This not only leaves plenty of bark for the tree's health, but keeps the letters distinct as the tree grows.
These markings may have been made by the same person as those encircled above for they are about the same depth, showing similar intricacy. It almost looks like a cartoon drawing. If this drawing had been deep enough to last it probably would have damaged the tree. The inner bark of a tree carries nutrients up the trunk. A carving this large might not leave enough bark for the tree to get the nutrients it needs for living, much less for healing. This is what is meant by girdling a tree - when the bark is removed all the way around the tree so that nutrients cannot travel to the top of the tree, much like puting a rubberband tightly around your finger.
Maybe it is a kind of oil. Instead of WD-40 it is WD-20.