The weevil (
charançon) hallmark was introduced January 13, 1864 for the marking of gold and silver items imported from countries with which France had signed reciprocal customs treaties. After June 28, 1893, and the creation of the weevil hallmark in an
oval frame, it was used only for the marking of gold items until its withdrawal on February 28, 1990. The X indicates the position of the assay office mark, which can help identify in which town the object was hallmarked.

I've included a clearer photo for reference.
