A book printed fifty years ago mentioned that in The Mona Lisa painting, there are symbols and characters painted inside the figure's eyes. The book was recently rediscoevered and the existence of the characters confirmed by Italy's National Committee for Cultural Heritage.
"In the right eye appear to be the letters LV which could well stand for his name Leonardo Da Vinci while in the left eye there are also symbols but they are not as defined.
He said: "It is very difficult to make them out clearly but they appear to be the letters CE or it could be the letter B - you have to remember the picture is almost 500 years old so it is not as sharp and clear as when first painted.
"While in the arch of the bridge in the background the number 72 can be seen, or it could be an L and the number 2."
See here: [Link]