Pardon the small correction, John... although I said it is a sprue, I said it is a mold filler hole sprue, not a mold vent hole sprue.
Unfortunately, I do not know the meaning of the "V" letter-mark. I note that it is not the usual serifed-letter stamped by a letter die -- but instead appears to have been made with the edge of a chisel in two simple straight-line strikes. That form at least "suggests" to me that it is a Roman numeral V. We often see Roman numeral marks on various civil war era cast metal objects, such as military belt buckles and sword-guards.
Regards,
Pete