Only one. The Madonna della Pietà (1498–1499), informally known as La Pietà, is a marble sculpture of Jesus and Mary at Mount Golgotha by Michelangelo Buonarroti, now in Saint Peter's Basilica, Vatican City. The statue was originally commissioned by a French cardinal, Jean Bilhères de Lagraulas, then the French ambassador in Rome. The Carrara marble sculpture was made for the cardinal's funeral monument but was moved to its current location, the first chapel on the north side after the entrance of the basilica, in the 18th century. It is the only piece Michelangelo ever signed.

Source: Wikipedia