The hamsa or "protecting hand" is believed to be a way of averting and getting protection from the evil eye, or in general, as a way of summoning assistance from the "Hand of G-d".
These pendants are hamsa amulets, ancient symbols picturing an opened hand with a palm and five outstretched fingers.
Many may use the Hebrew expression " bli ayin hara " (no evil eye) when they speak about their good fortune in an attempt to avoid its wrath against their good luck. It is believed that the envious glare of onlookers, even without any ill intentions, can cause divine repercussions.
It could be considered helpful to wear or display such an amulet from a totally practical point of view - simply to consistently remind oneself of our own fragility and weaknesses, and to help us reflect this realization in our day to day thoughts, speech and actions.