Postby silvermakersmarks » Mon Dec 11, 2017 9:47 am
Hi and welcome to the forum.
There is little doubt in my mind that this is a London hallmark and that the maker's initials are IS. I am having a little difficulty with the date letter but I suspect that it is most likely the d which was used from 6 June 1739 to 18 July 1739. My difficulty is in the shape of the punch which, if published sources are to be believed, should have a V-shaped lower part. However published sources are not always accurate with regard to punch shapes, but us this letter was used for such a short period I have not had the opportunity to see a confirmed example. I am not able to put a name to the maker as I am currently away from my references; perhaps one of our other contributors can check Grimwade to see if there is a matching mark consistent with this date.
Phil