The Magen David (Shield of David, or as it is more commonly known, the Star of David) is the symbol most commonly associated with Judaism today, but it is actually a relatively new Jewish symbol. It is supposed to represent the shape of King David's shield (or perhaps the emblem on it), but there is really no support for that claim in any early rabbinic literature. The symbol is not mentioned in rabbinic literature until the middle ages, and is so rare in early Jewish literature and artwork that art dealers suspect forgery if they find the symbol in early Jewish works.
The most commonly known and recognized piece of Jewish garb is actually the one with the least religious significance. The word yarmulke (usually, but not really correctly, pronounced yammica) is Yiddish. According to Leo Rosten's The Joys of Yiddish, it comes from a Tartar word meaning skullcap. According to some Orthodox and Chasidic rabbis I know, it comes from the Aramaic words "yerai malka" (fear of or respect for The King). The Hebrew word for this head covering is kippah (pronounced key-pah).
One of the oldest symbols of the Jewish faith is the menorah, a seven-branched candelabrum used in the Temple. The kohanim lit the menorah in the Sanctuary every evening and cleaned it out every morning, replacing the wicks and putting fresh olive oil into the cups. The illustration at left is based on instructions for construction of the menorah found in Ex. 25:31-40.
The Shema also commands us to bind the words to our hands and between our eyes. We do this by "laying tefillin," that is, by binding to our arms and foreheads leather pouches containing scrolls of Torah passages. The word "tefillin" is usually translated "phylacteries," although I don't much care for that term. "Phylacteries" isn't very enlightening if you don't already know what tefillin are, and the word "phylacteries" means "amulet," suggesting that tefillin are some kind of protective charm, which they are not.
On the doorposts of traditional Jewish homes (and many not-so-traditional homes!), you will find a small case like the one pictured at left. This case is commonly known as a mezuzah (Heb.: doorpost), because it is placed upon the doorposts of the house. The mezuzah is not, as some suppose, a good-luck charm, nor does it have any connection with the lamb's blood placed on the doorposts in Egypt. Rather, it is a constant reminder of G-d's presence and G-d's mitzvot.