This monogram is from heraldic artist Charles Demengeot, in his book Dictionnaire Chiffre-Monogramme, (1881). 

Monogram: AR

Accents/Accessories: Heavy oxidation; Detachable pavé diamond bail; Scalloped edges; Features lion; Raised monogram and details

Size: 89 x 52 millimeters (3.50 x 2.05 inches)

Weight: 41.70 grams (1.47 ounces)