Solve this Ca. 1790-1810 Mark & Win a Spoon or $15 Off Your Next Order

NOT FOR SALE - Here's a challenge - a circa 1790-1810 American coin silver tablespoon marked only IS in a large serrated punch, with a nicely engraved period script monogram of GJM and a V-shaped drop. This piece measures about 9 1/2 inches in length and weighs about 59 grams. It came in a lot with a piece by Caleb Bentley of DC, VA and MD, and it has the look of rural VA, MD or PA. I haven't seen this particular mark before, and am hoping someone else has. If you can solve this piece (or give me a very strong lead such as another piece with a known provenance going back and this same mark), I would be more than happy to either send you a nice coin silver spoon in good condition, or $15 off your next order with me. Thanks!