A fineness mark is a three-digit number. It indicates the minimum content of the marked precious metal in the article. The amount of precious metals is expressed in thousands; in other words; if a fineness marks reads 925, it indicates that the article in question consists 92.5 per cent silver. The fineness mark shield shape indicates the precious metal in questions.
The use of the shield around the digit is now voluntary. However, Tukes recommends that the shield be used for the sake of clarity. For example, palladium and platinum have similar finenesses, and different shield shapes are required for easier identification.