This pendant is made by the artisan from Jaipur in India.
It is a symbol of Om(Aum) in brass.
Brass is a good alternative to gold, it does not change color or decompose over time. It does not cause allergies, so you can wear it without fear. 
It is also very easy to clean by rubbing it with a little toothpaste and lemon juice.
 
Signification: 
Om: Concentration, Meditation.