Yes, it's Belgian, pre-1891/2.
The oval cartouche with star and ELG is the proof stamp of the Liége Proof house - Épreuve Liége.
18.2 - if it IS 18 - is the calibre in mm - in this case, it's 12g. It might be 16.2, in which case it's a very tight 16g.
The odd-looking curlicues are an intertwined E and L - ÉPREUVE LIÉGE - Liége Proof House.
The stamp that looks somewhat like a hammer is the Péronne, a Liége landmark - it looks a lot like Nelson's Column in London, but is much smaller.
The crown over a letter is an inspector's mark - it can be most any letter except j q o or w.
The letters GG are those of the assembler, and the cut marks are identifying marks used in assembly to keep all the components together.