Michelangelo is the only artist to have signed a major work in a fit of rage

Michelangelo signed the Pietà — his marble sculpture in St Peter's Basilica — after overhearing visitors credit it to another sculptor. He reportedly sneaked back at night and carved his name across Mary's sash: 'MICHAEL ANGELUS BONAROTUS FLORENT FACIEBAT'. It is the only work he ever signed, and he later said he regretted the vanity.

Source: Giorgio Vasari, 'Lives of the Artists' / Vatican Museums documentation