British law regarding the marking of imported watch cases was changed in 1907 by the "Assay of Imported Watch-Cases (Existing Stocks Exemption) Act", which required that all imported gold and silver watch cases had to be assayed and hallmarked in a British assay office.
The 19 laws regarding the hallmarking of imported gold and silver items did not apply to watch cases because the 1887 Act and Order in Council that had introduced the hallmarks with "Foreign" across the middle were not repealed by the 1904 Act and therefore remained in force.
The hallmark with a combination of a letter and a number is the date letter, that gives us the year of production.
This system for marking precious metalls started back in 1759 and is still in use, although the silversmiths are no longer obliged to use date letters.
Since there are many cities that starts with the same letter, there is a system where the letters have different style and are placed in different geometric forms.
Naturally there are quite a few city stamps, and many of them looks allmost the same.
Designer marks are unfortunatetly not that common on Swedish silver, and especially not on jewelry.