The rings on the bore vacuator are generally not kill rings,but used for identification as to what platoon the tank is in. Red = First PLT, White = Second PLT, Blue = Third PLT. Of course this is all up to unit Standard Operating Procedure (SOP). Not saying that they are not "kill" rings, but I've seen them on way to many tanks that have not been in combat. On the tanks that I've seen "kill" markings on they have been sillouettes of whatever it was they killed (ie. T-55, T-72, Truck, etc.) Generally, they have been only temporary and not allowed to stay on for very long (PC, Commanders guidance, etc).
The two M1's lost recently, in direct combat, were supposedly killed by an Air Defense Artillery gun at extremely close range AND from the rear into the engine deck during limited visibility (sandstorm). The Marine Corp M1 is believed to have lost sight of the tank to its front and missed the turn that the tank column had taken and therefore went over the edge of the bridge which did not have a guard rail on it (don't know why). The end result was that the crew drowned as the tank landed on its turret in about 40 feet of water. There was another combat loss but do not have any details off hand. It was during a "Thunder Run" into Baghdad after we had secured the Airport. Unsure if it was a combat kill, or damaged beyond repair and destroyed by another M1 to prevent it from fallind into somebody else's hands. There were many pictures and video of reporters and Iraqi's standing on a burned out hulk the next day. At least one M1 was destroyed this way in the first Gulf War (read "Tuskers" An Armor BN in the Gulf War. By David Pierson 4-64 AR).