The "FB" stamp that is found on some jewelry is the initials of the designer Francois Borgel. The stamp is usually followed by a picture of a key.
Francois Borgel was a businessman and inventor from Geneva. Borgel eventually grew a business that became a large manufacturer of Swiss watch cases, all of which bear the famous FB key trademark. Borgel was granted the first Swiss patent for his watch cases in Oct. 1891. After Borgel's death on March 7, 1912, the business was taken over by his daughter Louisa Borgel. In 1924, she sold the business to the Taubert family.