Please see the following link for an excellent overview of the French marking system:http://www.925-1000.com/Ffrench_marks.html
In France, as of June 19, 1798, makers were required by law to stamp their works with a mark in a lozenge-shaped reserve. The system in France for precious metals was highly regulated, so we do know when and where an object was made by the appearance of the marks.
The maker’s mark consisted of initials or name spelled out, and a symbol. In addition, there had to be other marks: the silver standard (poinçon de titre) and duty mark (poinçon de garantie). Therefore, if your object has a lozenge-shaped maker’s mark, it dates after 1798. We know the maker was Forget, and his working dates are first quarter of the nineteenth century. Eighteenth century pre-Revolutionary maker’s marks looked very different. I don’t know enough about watches to know whether the watchcase can post-date the watch mechanism, but your watch case is definitely not earlier than when Forget first registered his mark.
As for the horse’s head, this was one of those marks that had no regulatory significance, but carried over from the brief, chaotic post-Revolutionary period.
I can’t see the other mark you show well enough to identify it.
Hope this helps to clarify.