My plantologist side ventures that they're stylized olive branches. You will find few olive trees in Belgium, so I'd say they refer to peace.
Chrisild is quite right. The three squiggles are (left) unknown to me, (middle) the signature of Harry Elstrøm, the designer and (right) what looks like the head of Saint Michael, the mark of the Brussels Mint since the early 1500's.
Wikipedia (Dutch version) says: Elstrøm's father was a Danish industrialist, his mother a British author. In 1913, the family moved to Dresden, where young Mr. Elstrøm studied art at the technical university from 1918 to 1924. Immediately thereafter, he registered at the Academia Brittanica in Rome, Italy, where he participated in the excavation of Pompei. In 1928, he joined the Academy of Arts in Brussels. In 1934 he started his career as independent artist. Among his best known work is the crucifiction in the basilica of Koekelberg. He made over 300 statutes and plaquettes. Elstrøm also designed numerous medals, stamps and coins. He was renowned for his innovative work in the area of religious art. In 1940 he became sculpting teacher at the Sint Luke institute in Brussels and in 1952 he was appointed teacher in the architecture department of the royal university of Leuven.
Peter