The other day I saw a 91/30 with a strange marking on the receiver. It was etched in with maybe an elctropencil. It was on the receiver below the factory marking. It was a large diamond with a line intersecting the middle from top to bottom. The number 19 was etched on the left side of the diamond and the number 58 (or 59) was etched on the right side. I know the Soviets used a diamond stamp for refurbishments but I've never seen a mark like this etched into the rifle. I'm guessing the number may have been the year. Does anyone have any ideas on what this marking is?