Accepting that the Town Mark is the one for Chester an 1821 hallmark would also have carried a leopard's head and very probably a Duty Mark.This would leave the assay year as 1887 as you say but a trawl through Chester Gold & Silver Marks 1570 to 1962 by Ridgway & Priestley looking for J ? T marks comes up with the unsatisfactory result of:
JHT with pellets between the initials registered in 1882 by Joseph Hayes Taylor of 70 Spencer Street, Birmingham. The pencil has a loop for hanging from a chain and his entry notes show he made, amongst other things, "chain appendages";
JT with a large pellet between the initials registered in 1878 by James Thornton, a jeweller from 54 Guest Street, Hockley Hill, Birmingham.