Following AG2012 answer:
''In order to prevent and detect fraud of hallmarked silver articles, French authorities instituted, by Ordinance of 1st July 1818, a system of countermarks on the opposite side of the guarantee mark. These countermarks are known as "bigornes".
The term bigorne literally means two-horned anvil or two-beaked anvil and refers to the shape of the projecting ends of the anvil. Each anvil has two striking areas, one flat and one of rounded shape. The rounded horn served to mark hollowware and the flat horn was used to mark flatware.''