with the trapezoidal plate of course the symbol could include only one foot purely by way of indication the length of the symbol is of the order of 3 mm its largest width of the order of 1 50 mm and its total height including the feet is of the order of 0 75 mm such that the profile 10 shown in dotted lines in fig1 used to make it can have a rectangular section slightly greater than 3 u00d7 1 5 mm 2 it would also be possible to manufacture the same symbols from a profile having an isosceles trapezoid section slightly greater than the base of the symbols taking account of the diamondpolishing operations as will be seen hereinafter the method also enables symbols with no vertical flank to be manufactured faces 4 6 and 8 as well as ends 9 a 9 b having a rounded shape with reference now to fig4 to 7 an embodiment of the method according to the invention will now be described the rough material for manufacturing the symbols is formed by a profile 12 of rectangular section 10 it may be for example a gold bar 2 metres in length in a first step u201c a u201d shown in fig4 two feet 7 a 7 b are shaped using a face mill attached to a milling spindle 11 purely by way of indication the height of feet 7 a 7 b is greater than or equal to 0 03 mm and the diameter thereof.