The Second Series of Canal Zone stamps, commonly referred to as the 'U.S. Overprint Series', is composed of five United States stamps of the 1903 Series overprinted for use in the Canal Zone in the summer of 1904. Their purpose was to replace the First Series of overprinted Colombian stamps sold in June and July 1904 by the government of Panama to Americans for use on mail originating in the Canal Zone. Of a total of $390,000 face value in stamps, only slightly over $4,000 in stamps was ever sold. Collectors purchased the majority of those. Their first date of sale was July 18, 1904, and they remained available to the public only until December 11, 1904. No first day covers of this series are known, and the earliest postmark recorded on any of them is July 19.
A 1-cent stamp paid for a domestic postcard; the 2-cent paid for a first-class letter or foreign postcard; the 5-cent paid for international mail; the 8-cent paid for registry service or a two ounce foreign letter, and the 10-cent paid primarily for a registered first-class domestic letter. Singles and particularly combinations of these stamps used on 'real' mail—that is, not philatelic creations—are very scarce and quite expensive.
The implementation of the Taft Agreement, whereby the United States agreed to pay Panama 40 percent of the face value of its postage stamps, forced the December 11, 1904, removal of the series from the market. The stamps were then overprinted for Canal Zone use. The remainders of this series were burned in January 1906. The Taft Agreement remained in effect until July 1, 1924, when the use of Panamanian stamps was discontinued and overprinted United States stamps were once again placed into service.
