According to the Telegraph, Borgia said
the 50 year old volume describes how the Mona Lisa's eyes are full of various signs and symbols and he added: "We are only at the start of this investigation and we hope to be able to dig deeper into this mystery and reveal further details as soon as possible. It's remarkable that no-one has noticed these symbols before and from the preliminary investigations we have carried out we are confident they are not a mistake and were put there by the artist.Da Vinci's masterpiece has long been thought to be a portrait of Lisa del Giocondo, the wife of a very successful silk and fabric merchant in Florence, but with these letters and possible numbers (that don't seem to add up to LG), that long held belief may be called into question. The discovery of the figures, while enticing and thrilling to speculate on, have yet to reveal... what exactly they reveal - they could be obsolete and meaningless or they could unlock the secret to the real identity of the Mona Lisa. The painting is such an iconic work for a number of reasons, not least of which is how much mystery has always surrounded it. Dan Brown clearly chose his subject matter well.
(Image: Getty Images. Mona Lisa C.1503-5 Leonardo da Vinci(1452-1519 Italian) Oil On Wood Panel,Musee du Louvre, Paris, France)