A non-denominated 'F' stamp depicting a single tulip was issued on January 22, 1991, with an assigned postage value of twenty-nine cents. This was the Flower stamp, and it was issued in sheet, coil, and booklet formats. On the 'F' stamp, the term 'Domestic Mail' used on previous rate-change stamps was replaced with "For U.S. Addresses Only" as clarification that the stamp was valid for letters mailed within the U.S. but not for letters mailed in the U.S. to foreign destinations.
The printing was divided among three printing contractors.
The yellow, magenta, cyan, and black Flower sheet stamp (Scott 2517), designed by Wallace Marosek, was printed by the Jeffries Banknote Division of the United States Bank Note Corporation on an eight-color combination Andreotti-Giori gravure-intaglio webfed press and perforated 13 on an Ormag rotary perforator. The pane of one hundred, ten across and ten down, was printed from gravure printing cylinders of four hundred subjects. One group of four cylinder numbers preceded by the letter ‘U’ appears beside the corner stamp. “United States Postal Service 1991.” and “Use Correct ZIP Code.” are printed in the selvage.
The Bureau of Engraving and Printing produced the red, cyan, yellow, and black Flower coil stamp (Scott 2518) on a seven-color Andreotti gravure press (601) and perforated 10 vertically. It was distributed in coils of one hundred, five hundred, and 3,000. Printing cylinders of 432 subjects, eighteen across and twenty-four down, were used to print the coils of five hundred and 3,000; printing cylinders of 480 subjects, twenty across and twenty-four down, were used to print the coils of one hundred. One group of four cylinder numbers appears on every 24th stamp.
The Bureau of Engraving and Printing also printed the red, cyan, yellow, and black Flower booklet stamp (Scott 2519) in two formats—a booklet with a single pane of ten stamps and a booklet with two panes of ten stamps. Printed on the seven-color Andreotti gravure press (601), the stamps were perforated 11.2 on the Goebel booklet machine stroke perforator. One group of four cylinder numbers appears on each pane binding stub. Red electric-eye remnants appear on 10 percent of the binding stubs.
The final non-denominated 'F' stamp was printed by KCS Industries. The yellow, black, magenta, and cyan Flower booklet stamp (Scott 2520) was printed on the Champlain gravure presses at J.W. Fergusson, formatted in two panes of ten horizontal stamps, two stamps across and five down on the pane. The stamps were perforated 11 on the L perforator. One group of four cylinder numbers preceded by the letter ‘K’ appears on each pane binding stub. Magenta cut marks appear at the outer edge of the third stamp down on 20 percent of the panes.
Linn’s U.S. Stamp Yearbook 1991
Scott 2005 Specialized Catalogue of U.S. Stamps and Covers
Encyclopedia of United States Stamps and Stamp Collecting