This necklace has the "Shema Israel" blessing on it with the Jewish prayer inscribed on it in Hebrew which means "Hear, Israel, the Lord is our G-d, the Lord is One". The pendant uses an abbreviated and "modest" form of the prayer in order to allow it to be worn anywhere.
The Hamsa, also known as the hand of Miriam, is one of the original symbols for protection.
Kabala belief explains that the two triangles, interlocked in opposite directions, represent the contradictions in man; good vs. evil, spiritual vs. physical, and so forth. The upward point triangle symbolizes man's good deeds, which is directly towards to heaven. In turn, it activates a flow of goodness that comes back down to earth, and is depicted by the downward pointing triangle.