There are Two different "Sharpie Tests" that are being used. The have different purposes. This is what is called The Sharpie Test. It is used during fine grinding to insure that the tool and mirror are in 100% contact. This is important because without full contact reaching a Sphere is much harder and it would indicate a problem with the strokes being used. First you take the mirror and rinse it off and let it dry completely. You then take a permanent marker (such as a Sharpie - hence the name) and draw a grid pattern. I've used both Hash marks and a Star (or spoked) pattern, it doesn't matter. Make sure you let the marker dry.
