The "S" might refer to a woman in the Sforza dynasty that ruled Milan. The letter "L" could be for Leonardo.

The number 72 is auspicious in the Judaism's Kabbalah. 7 is also sacred in Judaism and Christianity in the creation of the world, while 2 could refer to the duality of man and woman.

But art historians aren't convinced of the meaning.

Claudio Strinati, art historian of Italian Culture Ministry, said, "Even conceding that there are really letters and numbers hidden in the painting, it seems to me that the mystery isn't emerging for these issue."

The Mona Lisa is a constant source of mystery. However unlocking her secrets could be a mystery that is never solved.