Better get a copy of Jackson's hallmarks which is pretty much the definitive guide. Towns and cities with current assay offices should list them in local directories
London, Sheffield, Birmingham, Edinburgh are the only ones operating now but there were offices in Bristol, Chester, and Glasgow in the past.
The link posted (twice) above might well answer your question.
However, if you want to post a photo, go here
https://postimages.org/
Upload your photo, copy the first link in the list that you'll then see and paste it into a post here on AB. (It's best to put it on a separate line to any other text). We'll then be able to click on the link to view your photo.