Debt of Blood
The Cossacks paint their machines a flat rust-red color. Traditionally, each MechWarrior gives his BattleMech a name, which is painted across the back of the machine in Russian.
Per FM: Merc (revised), page 81.
Other references:
Victor, FM: Mercenaries (plate 14)
The force insignia is a Cossack horseman riding out of a golden circular field and wielding a flaming saber. This emblem is painted across the right torsos of unit BattleMechs and the left fuselage sides of aerospace fighters. Per FM:Mercenaries Revised, page 81.