The information regarding Saunier(-Miéville) is from the recent book by Christian Hörack,
L’Argenterie Lausannoise des XVIIIe et XIXe Siècles
 (Lausanne: Musée Historique, 2007), pp. 66-67 & 254, which I posted in an extensive thread about Swiss silver in different silver forum.
I made an error there; the father of François Saunier-Miéville (1804-1876/77), Louis-Marc-Samuel Saunier (1769-1845), was not French but of French descent. He was born in Nyon, canton Vaud, Switzerland and had moved to Lausanne by 1774. No works by him survive nor are any of his marks known, but a 1794 design for a censer by him does survive; it is illustrated in Hörack, p. 103.
The younger Saunier added the “Miéville” to his name when he married Marie Miéville, a widow with a young daughter. Saunier presumably added the hyphenate so that he and his new step-daughter would have the same surname.
Lausanne did not have any formal guild, so precise working dates for the silversmiths there are difficult to determine. Hörack gives working dates for Saunier-Miéville of 1839-1846, and notes that he also worked later as a salt factor, a doorman, and (by 1870) a jeweler. (He did not become a citizen of Lausanne - in the legal sense - until 1860.) All of Saunier-Miéville’s works illustrated by Hörack (a cream jug, a sugar sifter and a teapot) date to aruond 1840; also illustrated is a trade card (carte de visite), which I can try to scan and post, if anyone is interested.
Hörack lists, in addition to the “FS” mark here, two other marks of Saunier-Miéville: “SAUNIER” and “F:SAUNIER/A LAUSANNE” (the latter incuse). Two variant city marks are also noted; again, as there was no guild control of marking, these vary in design from maker to maker. Regarding the apparent dissimilarity of the city arms as they appear in the mark and the web illustration, it is to be noted that the tinctures (coloring) of the Lausanne arms - “gules, a chief argent” — are indicated by the traditional rules of
hatching: gules by vertical lines, argent by no hatching at all.
Hope this helps!