By the end of 1867 the alphabet had been used in full and the diamond mark had to be altered to avoid repetition.
This means that the letters and numbers used to represent dates are at different points of the diamond between 1842-18-1883.
Diamond marks were issued by the Patent Office between 18.
They were issued with the registration number when a design was registered.
Use this guide to find original representations (drawings, paintings, photographs) of trade marks.