Da Vinci Used Hidden Info as Copyright Protection

I happily feel like a last of the literary Mohicans for not reading Dan Brown's The Da Vinci Code. It's catching dust somewhere on my book shelves, though this little news article on an exhibition of Da Vinci's mechanic's may make me skim a few of its pages:

"Computer graphics have enabled the discovery of hidden information" in Da Vinci's multitude of technical drawings and "made it possible to make them work by computer simulation," said Italian cabinet-maker and mechanic Nicolai Gabriele.

[...]

Asked about Dan Brown's worldwide bestseller, "The Da Vinci Code", Gabriele drew a parallel between the secrets or mysteries which the books says Leonardo liked to hide in some paintings like "The last Supper", and small details in his technological sketches.

Such details were apparently aimed at preventing undue use of his discoveries, centuries before the concept of patents and copyright was born.