Mark Edges to be Cut

If I'm working on a bunch of identical parts and I need to cut or machine both sides I often find it difficult to keep 'em sorted out so I know which side I just cut. So, I'll just spray a light coat of paint on one side. Then, I can cut the other side, and even if I drop some of them or get them mixed up, I'll have no trouble figuring out which side gets cut next.
