FINE CENTERING. A RARE USED EXAMPLE OF THE 6-CENT 1895 "USIR" WATERMARK ERROR. ONLY 29 ARE KNOWN TO US.
The "USIR" (United States Internal Revenue) watermark error occurred when a supply of paper reserved for revenue stamp production was used for printing the 6c and 8c postage stamps. Our updated census of this issue, published at http://www.siegelauctions.com/dynamic/census/271a/271a.pdf , records only 27 used copies certified as genuine by the Philatelic Foundation, plus two uncertified copies. Eighteen of those certified do not specify which letter is present. Many examples have perfs either close or touching the design.
Census No. 271a-CAN-25. Signed Sloane and with 2010 P.F. certificate.