Gil, until we have the serial number and proof marks were just guessing.
All, The A5 safety originally called the 'suicide safety' was a different design. It was within the trigger opening, but not set in the front of the trigger guard like were talking about. It was discontinued before Belgian 16's were introduced in the US.
The big problem with the "trigger guard" safety in question is they can be hard to get off in a hurry, like on flushing game. I have a pile of them and still struggle with them a bit.
http://pg.photos.yahoo.com/ph/jeffmulliken/detail?.dir=40abre2&.dnm=5664re2.jpg&.src=ph A lot of these safeties were converted by Browning to the cross block safety. The Browning factory manual includes gunsmith instruction on this conversion.
Jeff
