And many centuries later, that is how we hang our mezuzot today. While many people suffice with a mezuzah on the front door of their home, the actual requirement is to place one on each doorpost inside the house as well. A mezuzah goes in every room except the bathroom, laundry room or closet. A kosher mezuzah is one that has a hand-written parchment inside of it. Mezuzot that contain printed texts are not considered kosher or in fulfillment of the mitzvah.
Some people have the custom of kissing the mezuzah when they walk in or out of a room or home.
This is an act of affection, not required by Jewish law, but voluntarily assumed by many. Not long ago, I read about a synagogue that affixed a second mezuzah on the front door of the shul, about halfway down the door, so that small children and people in wheelchairs might be able to reach the mezuzah and kiss it. That's a lovely idea, and one that I hope to enact when we construct our new synagogue entrance next year. However, it has become common practice to voluntarily extend the presence of mezuzot to these Jewish places. Shin stands for Shaddai, one of the names of God, and reflects the belief and hope that a house on which hang mezuzot will know both God's Presence and Protection.