According to Tardy p328, letter G in a square with cut corners has been used between 1866 and 1919 in the city of Gmünden, Poland, during the austro-hungarian period.
Hallo dinio,
the mark looks indeed like the mark of Gmünden in Tardy, p 328. But I think, theoderichs note is right, that the spoon is older. I think, it is from the first half of the 19. century.
The "G" here is the city mark of St. Gallen, Switzerland. The maker "SSC" is Silvester Samuel Cunz (1760-1839), and "RIETMANN" is Michael Rietmann (1782-1862).