This is signed "Prince de la Moskowa". but it's not the heroic Marshal Ney. It's his son, Napoleon-Joseph Ney (many of Napoleon's marshals named their sons after the emperor - there must have been a lot of young Napoleons in France at one point).
But why is it so interesting? Because he was a believer in homeopathy.
And he was able to call on the services of a pioneer of homeopathy, the Belgian physician Baron Seutin to come to the aid of his valet.
Not every prince would take such pains for his valet, but he was obviously his father's son in his concern for those who served him.
Really quite an exciting piece of "alternative medical" history.