Vinci is a town in Tuscany, Italy, and the birthplace of the famous artist Leonardo da Vinci.
It is commonly thought of and used as Leonardo da Vinci's last name. However, Leonardo did not have a last name (as people didn't in those times) and it was simply used as a way of identifying the region where Leonardo came from to distinguish him from other Leonardos.
Knowledgeable/credible historians always refer to the artist as simply "Leonardo" or "Leonardo da Vinci" but never "Da Vinci".
Dan Brown, the author of "The Da Vinci Code", displays his ignorance and lack of credibility by using the term "Da Vinci" in his book to refer to the famous artist, Leonardo da Vinci, as though it was his full name.