Here's one that appears in the 'Unregistered Section' of Grimwades. Thought to be the mark of Joseph Bell II (Grimwade 3624)Photo courtesy of Chris
The mark was struck on a tablespoon (8 1/4" - 20.96cm) assayed at London in 1758, the same year and type of item that was noted by Arthur Grimwade.
Joseph Bell entered his mark (Grimwade 1132) with the London Company as a Largeworker on the 25th October 1756. The mark shown above could have been entered into the missing Smallworkers register (1739-1758), (although officially tablespoons came into the category of Largework) or it may have been entered into the missing Largeworkers register (1758-1773) or it may possibly never have been registered at all.
Another possibility is that it may be the mark of Joshua Bell, who Heal records working in Carey Street in 1756.