Prussian, Customs Seal, Stassfurt, Image & Found by Ashleigh Floyer.
Found by the coast in the state of Victoria, Australia, 22mm.
Monogram that looks like
Frederick William II in border of eagles displayed // S. STA. / NEU / STASS / FURT in border of eagles displayed
From Jan van Oostveen, "This is a custom (ST.A abbrevation) seal and can be dated in het 19th century (< 1840)."