The 15-cent Webster was the last stamp of the Continental Bank Note 1873 Issue with a discernible 'secret' mark. The secret is the small amount of plate wear at bottom and center, between the ‘1’ and the ‘N’ of ‘FIFTEEN’ and also replicated symmetrically between the ‘5’ and the ‘C’. The National Bank Note 15-cent Webster has more clear and distinct lines in this area and has a darker and clearer orange color ink overall. The CBNCo printing employs a lighter yellowish-orange color. As with the 12-cent stamps, the NBNCo and CBNCo printings of this 15-cent issue are more easily discerned by directly comparing the two stamps.
Like other stamps of this series, the 15-cent Webster had more uses after the adoption of Universal Postal Union rates. Before 1875, the stamp could pay the five-times domestic rate or, in combination with other stamps, the large foreign destination rates. After the U.P.U. rate was put into effect, the stamp conveniently paid both the registered fee and the U.P.U. five-cent rate for a single letter. Continental Bank Note Company printed approximately 2,050,000 stamps of the 15-cent Webster issue.