The majority of artists use a signature, name, monogram or some other identifying mark on most or all of their work. However, signing a work is not required, and a minority of artists choose to leave their work unsigned. While signing artwork is now thought of as normal, artists explicitly putting their own names on their work is a relatively new phenomenon.
Ancient artists rarely signed their work. Most modern ideas about who created ancient works of art come from writings or inscriptions from the same time period. The famous sculpture Venus de Milo, for instance, is typically attributed to Alexandros of Antioch on the Meander, while others assert Praxiteles, another famous ancient Greek sculptor, was responsible for the work.
Prior to the renaissance, it was uncommon for artists to sign their works at all. Most modern people think of an artist as a single person creating a single artwork, but in earlier eras, artistic works were produced in workshops, often with several or even dozens of workers contributing to the same piece. In these cases, the lead artist of the workshop affixed his name to the work, while the apprentices and helpers went unnoticed. While this seems like an antiquated idea, Andy Warhol's "Factory" of the mid-20th century worked in much the same way.
Renaissance and baroque masters such as Michelangelo, Albrecht Durer and Caravaggio began signing their own names to work they created entirely by themselves, a trend which remains the norm today.