A method of forming a three-dimensional article includes sequentially forming a plurality of first two-dimensional layers and a second two-dimensional layer. The second two-dimensional layer includes a second outer edge and a second inner area within the boundary defined by the second outer edge. The second inner area includes uniform physical characteristic and a watermark area within the second inner area having a physical characteristic different from that of the second inner area. An article includes a body with an inner area having a physical characteristic. A watermark is within the inner area and has a physical characteristic different from the physical characteristic of the inner area.