Thanks for the update — pleasing to have the two examples and to be able to confirm that it is indeed the DS crowned mark with a pellet below.
I now realise why I thought I had seen the mark before. I actually have it on a pair of trefid sweetmeat forks that I picked up a few years ago. Sorry the penny didn’t drop sooner. By their style I would date my forks and yours to c.1695.

I must say I still suspect that the items from which the marks in Jackson were taken may actually have been later than 1660/70. I would be very hesitant about ascribing a trefid to the 1660s without a date letter or firm knowledge of the maker’s working period. However, a working life of 30 to 40 years or more is certainly feasible even when general life expectancy was shorter than now.Anyhow, whether or not the dates in Jackson are correct, it is the same mark.