It is a very old custom that the back of a mezuzah has Hashem’s name (Shakai) written on it. Sometimes the margin of the mezuzah is too large and when the mezuzah is rolled, it covers the shem. It is brought down that when we walk by the mezuzah we put our hand on the shem and kiss our hand, in the same way that people kiss the sefer torah. The best way to do this is if you actually see the letters of Hashem’s name. Some people make a window by cutting the klaf as shown in the above picture, but it is better to simply fold the klaf. I asked Reb Wosner if it is really better to cut a window in the klaf than to just cut the margin of the klaf down a bit. He agreed that once you are cutting the klaf it hardly makes a difference if you are cutting a window or cutting the whole margin. Sometimes instead of cutting the klaf or making a window, people fold the edge of the klaf. This is the most preferable method. If you have mezuzos and you need help folding them please call me. For a small charge I will neatly roll up your mezuzos and put them in the cases. If you would like to see how I roll mezuzos watch my video in How To Roll A Mezuzah.