in 1700 hundreds H was the citymark for Hadeerslev afterwards a bridge was the citymark.
Jens Jensen Due was born 1738 working from 1761 in Odense, Flensborg and Riga, From 1764 in Sønderborg from 23 march 1767 in Haderslev gets citienship june 16th 1768 dead 1810 in Copenhagen.
The hallmark you show - I cannot find. So its a wild guess.
However he uses a JD - different from yours but still it has some similarities. Its definetly not the mark you show but he could have had other in his carrier,
Is last quarter of 1700dreds possible? You show no picture of item.