Chai

This is spelled wrong, what it's meant to read is Chai, not "Hi":

This symbol, commonly seen on necklaces and other jewelry and ornaments, is simply the Hebrew word Chai (living), with the two Hebrew letters Chet and Yod attached to each other. Some say it refers to the Living G-d; others say it simply reflects Judaism's focus on the importance of life. Whatever the reason, the concept of chai is important in Jewish culture. The typical Jewish toast is l'chayim (to life). Gifts to charity are routinely given in multiples of 18 (the numeric value of the word Chai).

Hamesh Hand
The hamesh hand or hamsa hand is a popular motif in Jewish jewelry. Go into any Jewish gift shop and you will find necklaces and bracelets bearing this inverted hand with thumb and pinky pointing outward. The design commonly has an eye in the center of the hand or various Jewish letters in the middle.

There is nothing exclusively Jewish about the hamesh hand. Arab cultures often refer to it as the Hand of Fatima, which represents the Hand of G-d. Similar designs are common in many cultures. Why it has become such a popular symbol among Jews? I haven't been able to find an adequate explanation anywhere. My best guess: in many cultures, this hand pattern represents a protection against the evil eye, and the evil eye has historically been a popular superstition among Jews.