I have been informed by Dominic, a friend collector from another forum, that ISB stands for Isaac Schimmel Busch, an armourer from Solingen.
I haven't been able to find any further info on him.
Does any other friendly forumite have any info on this armourer?
Dom also informed me he doesn't believe this is a Dutch sword. The only other alternative as I see it is perhaps Belgian.
Any thoughts on the matter?
Best
Manuel