You are looking at a St. Anne fourth class badge instituted on November 12, 1796 and founded by Emperor Paul I. This was actually a subsidiary or Fourth Class of the Order of Saint Anne for non-commissioned officers and enlisted men.
The lowest (4th) class of the order was usually called "St. Anne's Weapon Order". A small badge of the order was attached to a steel edged weapon (appropriate to the branch of service of the recipient) inscribed "For Gallantry." The gold edged red ribbon of the order made up the sword knot.
Most of such pieces were removed from swords after the Russian Bolshevik revolution in 1917 and not many survived till our days.
Slight enamel chipped, otherwise in good condition. Original and rare.