"Counterfeit Detection Guide" . This is a great pocket guide written by Bill Fivaz.   I used it while looking for a 3-Legged Buffalo Nickel. As you can see there are 4 main characteristics to a real 3-Legged Buffalo.  The one, to me that really stands out is what looks like a "pee-pee" stream leading down from the Buffalo's belly to the ground. Also that 3rd leg is missing but the hoof remains.