Easy.
The markings show 1.81g (gram) of Powder (28 grains= 1 dram) and 24.5g of lead shot (about 7/8oz).
This is a 16 ga shotgun. Those are service loads and not proof loads.
This is a very unusual marking for a Belgian shotgun.
AFAIK, only Manufrance (or rather Manufacture d'armes et cycles de St-Etienne) used to print those on the barrels flats, along with the proof loads.

Best regards,
WC-