The mark next to the "D" in UNITED, it that round? If so it was made from a split plating issue. If it is a split plating issue, then the plating was there at one time, now removed. If the color I see there is copper, then it was removed. Sometimes the plating is covered with a plating of zinc over the copper plating. The surface is usually rough looking.

Note the copper area next to the rim on my coin.