I've cracked the real da Vinci code! The term "mona lisa" is a play on words indicating "my smile". And "La Gioconda" means "the joking", "the joke", or "the happy".

The Mona Lisa is wearing Spanish clothes. Smile is sonrisa in Spanish. Sonrisa - risa - Lisa - like Cockney rhyming slang or even Polari. Mona is a latinate play on mio or mon (my). Gioconda is the same as joconde in French and jocund in English - all meaning "of a humorous temperament".

None of this is at all far-fetched when Leonardo da Vinci's relationship with his transgender lover Salai is taken into consideration. Mainstream scholarship has long understood the amorous nature of Leonardo's relationship with Salai. See the pornographic image below for evidence of this. 

I believe that in the 19th century, after a newfound appreciation of Michelangelo and Leonardo da Vinci replaced widespread veneration of Raphael, and as societal and money power shifted from Catholicism to Freemasonry, a curious appreciation for the Mona Lisa grew amongst those "in the know", who knew the true significance of the iconography of the Mona Lisa. 

First we must consider that the primary deity of Freemasonry and Kabbalah is a composite god  - Isisosiris or Zion (Zi = Isis and On = Osiris)  - which is basically a deification of the unity of the sexes, as is symbolized in the Seal of Solomon, which in turn is said to be representative of the contents of the Arc of The Convenant (sacred sexual union). So the Freemasons / Zionists actually worship what I have denominated The Sacred Hermaphrodite -- though many of them are unaware of this. The Masons, Zionists (Zionism is an ideology espoused by many Jews but not exclusive to them as a group) and generally cultured people who were aware of the true meaning of the Mona Lisa - that it portrayed an icon of apotheosized hermaphroditism - therefore joked about it having an "ambiguous", "mysterious", "enigmatic" smile. The enigma is that the subject is sexually ambiguous!

Why else would the art canon have given precedence to the Mona Lisa above all Leonardo's other paintings? And why did Leonardo paint several copies of the Mona Lisa if it was just a portrait of an aristocrat - did he do that for other patrons as well?

Consider the following Wikipedia information:

- Leonardo had no income during the spring of 1503, which may in part explain his interest in a private portrait.

- He was not paid for the work and did not deliver it to his client.

- An acquaintance of at least some of Francesco's family,[11] Giorgio Vasari wrote, "Leonardo undertook to paint, for Francesco del Giocondo, the portrait of Mona Lisa, his wife" (Italian: Prese Lionardo a fare per Francesco del Giocondo il ritratto di mona Lisa sua moglie.). (NB Giorgio Vasari was the first major art historian of the Renaissance).

- Speculation assigned Lisa's name to at least four different paintings and her identity to at least ten different people.

So da Vinci painted more than one Mona Lisa. Was it common practice to paint multiple portraits of the same person in the same pose?

I think that the answer to the enigma is that those "in the know" have always been fully aware that the Mona Lisa was a self-portrait of Leonardo da Vinci himself in drag dressed as a woman. As the painting became increasingly popular in the 19th and 20th centuries, the joke must have gained monumental status among the illuminated members of society, as they watched hoards of masses of onlookers gaze perplexed at the strange beauty hanging before them on the wall of the L'ouvre, each one of them wondering why the painting was so famous. 

Drag is nothing new, and has always been employed as a burlesque. I suspect Marcel Duchamp may have even been parodying the Mona Lisa to some extent when he donned his Rrose Selavy drag persona. 

Transvestitism is generally an attempt to harness the power of both sexes, although as a manifestation of gender unity it is inferior to true regal decorative embodiment of sexual union - the kind achieved by Indian maharjas, Louis XIV, Queen Elizabeth I, and certain pop stars like David Bowie.