During the period 1842-1883 the British Patent Office issued a diamond mark along with the registration number when a design was registered.
As well as showing that the design had been registered, diamond mark offered the buyer the reassurance of knowing an item was of British design. It also assured the person registering the design a degree of protection from copying. The protection was dependent on the type of material and the class in which the product was placed.
The mark was created to identify the type of material used (known as the class), how many items were included, (sometimes known as bundles or packages, and the date of registration.
Note that the registration number does not form part of the mark.
The centre is occupied by the abbreviation Rd signifying that this is a Patent Office mark standing for Registered Design.