I haven't been able to find the maker of this tastevin hallmarked for 1798-1809, maker's mark L S in a diamond with a rectangular object in between. The inscription is G P Dumon 1805.
This is not a Parisian maker (as evidenced by the provincial first standard rooster with the "1" on the left), so you will first need to identify the assay office. You need to clean the guarantee mark (the mark in the center of your third image, to the right of the rooster) and see if you can identify the numbers to the left and right of the man's head. This will identify the departmental assay office, which will reveal where to start looking for the maker.
As I've mentioned before, the numbers in French marks correspond to the official départemental numbers of each particular regime; the assay office numbers used in the first three post-revolutionary series of marks – First Republic (1798-1809), Empire (1809-1819), and Restauration (1819-1838) – are all different, and you must make sure that you are checking the appropriate table of assay office/département numbers corresponding to the particular series of marks. (Tardy gives only the 1819-1813 table.)
Département 50 in 1798/1809 was Loiret (not Haute Marne), and its assay office in Orléans. I checked Nicole Verlet-Réaubourg's Orfèvres d'Orléans and, yes, it shows that the mark on your tastevin is that of Louis Sionnest (1743-1811; master 1769) of Orléans.