that's a great little piece Robin - lovely enamelling too. Well you know what they say - .....separated by a common language etc.
- but we do usually call such mechanically acid applied details as a backstamp - would be great had it been compulsory - we'd almost be redundant.
Starting c. 1840, the British Board of Trade offered some degree of protection to inventors of new designs, by providing a system of Registration for each specific design/Registrant. This covered not only designs from within this country, but also I think for designs from outside the U.K., but where these were being sold or promoted within Britain.
This was a numerical system - arranged around a core of 13 CLASSES of materials - wood, metal, glass, ceramics etc., and provided the design was not an infringement of someone else's creation the a No. would be allocated which provided protection (of sorts) for a period of three years.
Initially, when the item in question was made, and where possible it included details of the date of the design, the CLASS and a Parcel No. - and these details were shown in the form of a diamond lozenge. This system lasted until c. 1884, when the diamond was dropped in favour of using a single No. - if known this can be checked and can provide details of date of Registration and Registrant. Original factory drawings (in the case of glass, wood, metal etc.) can be viewed at the National Archives, and we have permission to reproduce these images on the GMB.
Yes, believe there are some 'master salts' than can be considerably larger than most that we're accustomed to seeing.
In the next hour or so I'll add the National Archive copy of the factory drawing for your sweet. Some designs such as Stratford Rings and Woodchester ticked on for eons - the former still going strong apparently c. 1970 - and new shapes were added frequently from 1921 onwards, although none ever looked as good as these early enamelled pieces - the spiders webb cocktail shaker always comes to mind.