The guild city mark of Gorinchem (province (zuid)Holland) has been based upon two crenelated beams in a shield with a crown but also seen without crown. At the end of the 18th century the two crenelated beams were simplified into a wave pattern. Gorinchem is pronounced Gorcum and often spelled Gorcum.
The maker’s mark IS for; Jacobus Schrader Sr registered in Gorcum from 1773-1811. Known flatware maker.
The crowned date letter for 2 st standard of silver 875/1000 fineness, X for 1780 or 1804.
Could you show us an image of the complete spoon and all marks?
Oel