"To the naked the symbols are not visible but with a magnifying glass they can clearly be seen," said Silvano Vinceti, president of the Committee.
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."
The painting also featured in the Dan Brown blockbuster The Da Vinci Code, which was turned into a 2006 film starring Tom Hanks. His character interprets secret messages hidden in the Mona Lisa and Da Vinci's other works, including The Last Supper.
"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."
Mr Vinceti is part of the group asking French authorities for permission to exhume Da Vinci's remains from his tomb at Amboise Castle in the Loire Valley.
”We also know that Da Vinci was very esoteric and used symbols in his work to give out messages and we have examined other paintings and have not found any similar numbers or letters.
”Painters we have spoken to have also said they are unlikely to have been put there by mistake so we are confident that they are a message from Da Vinci and were specifically inserted into the eyes by him.
”What adds to the intrigue is that they are in the pupils, the darkest part of the eyes, so they would only be none by him - if he had wanted them to be more widely seen then he would have put them into the more visible white parts of the eyes.
”The question now is what to they mean - we are fairly confident that the LV is probably his signature but the other numbers and letters? Who knows they may even possibly be a love message to the figure in the painting.”