In the years from 1842 to 1883 were used English registry diamond-shaped marks. After that, a system consisting of the letters "Rd No" followed by a number was introduced.

 In January 1884, registered designs, trademarks and patents began to be identified by a system of sequential numbers. Please remember that ceramic articles represented only a small part of the registered products (shapes or designs). The table below shows the approximate numbers from each year. Using these numbers, one can just estimate the year of registration (the earliest year of manufacture). Registered shapes and designs were usually used in subsequent years as well. The table below is based on data from Kovels.