What was the only piece of art that Michelangelo ever signed?

The only work that Michelangelo actually put his signature on is
also one of his most famous, Pieta, in St. Peter's Basilica in Rome. He
spent three years on it, from 1497 - 1500.  Pieta translates into "Pity", and is a Christian
artistic theme from the Renaissance Era that depicts Mary holding the slain Body of Christ.  Some
believe that Michelangelo signed this particular work (on a sculpted ribbon across Mary's breast,
no less)--which he obviously never did with any of his other pieces--because he was so satisfied
with how the sculpture turned out, but most historians attribute this rare signature to
Michelangelo overhearing someone in the Basilica attribute the sculpture to someone else, and
that he did it out of pride.  There are references in later written works that Michelangelo
regretted doing so.