A Minion's Scourgestone is the insignia of the Scourge rank and file. These are sometimes found on the weaker of their troops positioned in the Plaguelands, though the term "weaker" is certainly to be considered in context. The Scourge, no matter where they are, should never be underestimated. The Argent Dawn currently offers a valor token in exchange for twenty of these insignia - an exchange I'm happy to do, provided you have earned enough scourgestones!