GB means George Burrows to most tong collecters , George Baskerville to wildly optimistic dealers — and a worry look for most of us . There are a lot of GB marks out there and trying to sort them out is usually a nightmare.
One GB that appears regularly on buckles of the 1765 —1784 period is the hooked GB. (The top of the "G" has a very pronounced hooked serif )
It is so distinctive that I trawled right through all the George Burrow, George Butler and George Burnett entries at Goldsmiths Hall to see whose it was.
None of them. No Register entry matches.
The left mark is on a shoe buckle, the right on an unusual pattern stock buckle.
Both have London type Lions of the 1756 —1784 type.
I have no suggestions for the identity of this maker, but he seems to have stopped work by 1784 as I've never seen one of his marks associated with a Duty mark. Most of his buckle are a little bit out of the ordinary - but I can find no provincial makers that fit and I'm 90% sure he's London