These initials are often found cast into the bedplates and comb bases of Swiss musical boxes. They stand for Société Billon et Isaac or, to give the full name, Société Anonyme Libre de L´Ancienne Maison Billon et Isaac, set up as such on 1 January 1867, in Geneva. See also Billon-Haller, Jean.
(Ord-Hume, Music Box, 1980, p. 331)