This is a dognose teaspoon made c.1700, possibly before the Britannia standard came in because of the first and second name maker's mark of SB with a four legged animal above. It's not in Grimwade or Jackson's which is strange for such a distinctive mark. I wonder if the dog could be a rebus for Barker. Just a thought!
It's not a mark I recall seeing before. The shape of the stem makes me doubt whether it is pre-1697. The early dognose spoons tend to have broad, flat stems much like those on contemporaneous trefids so my guess is a late provincial example - but an intriguing mark. Wish I could help, but I like your suggestion!