The face traced by Michelangelo

In piazza della Signoria, just in front of  Palazzo Vecchio, you can go in search of a strange legacy left by Michelangelo Buonarroti which is not so easy to spot and has a strange story attached to it.  
Standing in front of the stairs which enter Palazzo Vecchio, look to the right and on the wall behind the sculpture of Ercole and Caco and almost in the corner of the building, if you look closely, you may see sketchy outline of a man’s face traced on the wall.  This portrait is attributed to Michelangelo Buonarroti,  but no-one knows who the face belongs to: some say it was a nuisance of a man who pestered Michelangelo every time he saw him with questions and requests, or perhaps it was the face of someone sentenced to the stocks.