The symbol "A1" on silverware is a marking used to indicate the number of ounces of pure silver used in the plating process. The marks used on silverware vary by country.
On the reverse side of silverware, one can usually find one or more indented marks. These marks are used to determine what the item is made out of and sometimes where, when and by whom it was made. British electroplaters used letter codes for plated ware. The highest quality used is A1 or AI followed by A, the next levels are B and C, and the lowest level used is D.