This is an MC Gregory mouthpiece for the alto sax, serial number 5947. It's the Model A, a late 1930's vintage mouthpiece made famous by Paul Desmond. It is stamped 5A20, meaning it has a tip opening of 5 and a large chamber.
The condition of the piece is excellent. The bite plate has hardly a scratch on it. The gold lettering shows no wear. There are a couple scratches on the top and table of the mouthpiece from a ligature, but these are merely superficial.
The sound is very controlled and focused. The mouthpiece has a little resistance to it, which seems to very slightly darken the tone. This is a fantastic piece that will satisfy many professional players.