In Muslim tradition, Hamsa is known as the Hand of Fatima,
which refers to Fatima Zahra, the daughter of Mohamed, the
prophet of Islam. According to folklore, Fatima was stirring hot
milk when her husband suddenly came in with another woman.
Fatima was so shocked that as her spoon fell into the stew.
Fatima without noticing, kept on stirring using her own hand.
The tear that Fatima shed has worn the image of the eye. The
eye is often fixed at the middle of the Hamsa is believed to
provide strong protection against negative energies.

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In some Middle Eastern countries people also wear it as a symbol of equalities between Jewish and Muslim people. The hand symbol can also be found in Jewish culture, and therefor it is a very symbolic link between the two groups. I got a hand-necklace from my mom in Kusadasi 8 years ago and never took it off ever since