Need Help Identifying an Art Nouveau Tray Maker

I need help to identify the maker of an Art Nouveau Tray. The Tray is hand crafted and is signed with hand engraved marks “KRX, 3757” and has a Hallmark on one handle of the letter “F”. I don’t know what type of metal it is, it looks like sterling silver. The Tray is cast and has hand engraved details. Overall dimensions are 11 1/2" x 8 3/4" x 2" high. Does anyone know the maker? Thank you!