Winchester73 you are right... the CS-3 mark is exactly where you indicated (see picture).
The D1 picture is the "Wischo" mark, the German importer of the 686 Security Special revolvers (the Italian mark due to the import of this handgun in Italy is engraved near the grip with the italian identification number - 3324).
The D4 mark is the CS-3 mark to indentify the customization made in S&W plant by Custom Service.
The D3 mark? What's? The "S"?
Last edited by drag71; January 8, 2013 at 02:58 PM.