On the right-hand doorposts of traditional Jewish homes (and many not-so-traditional ones), you will find a small rectangular shaped case like this one. This case is commonly known as a mezuzah, because it is placed upon the doorposts of the house.
"And you shall write them on the pillars of your house and on your gates" (Deuteronomy 6: 9).
The mezuzah serves as a constant reminder of God’s presence and commandments. The Hebrew letter 'shin' is usually seen on the outside of a mezuzah representing the 'Sh' in "Shaddai," one of the names of God, reminding us that God watches over the home. The wording on the parchment the mezuzah protects is taken from the Shema Yisrael ("Hear O Israel") prayer. (Deuteronomy 6:4-9; 11:13-21).
This mezuzah depicts the two tablets of the 10 commandments, with the Hebrew letters above them.