An upcoming U.S. commemorative with an unusual "stamp on stamp" motif will honor World Stamp Expo '89, the first international stamp show directly sponsored by the U.S. Postal Service. The show will take place in Washington Nov. 17 through Dec. 3.

The new stamp is a vertical design. Its upper portion is gray and features "World Stamp Expo '89" in white letters and "25 USA" in black. Occupying the lower portion is the "stamp on stamp," the classic 90-cent Abraham Lincoln stamp. It has an engraved black-and-white vignette of Lincoln, with an ornate carmine border. An interesting feature of the new issue is a reproduction of a typical 1869 cancellation.There are two ways in which collectors may obtain first-day cancellations. In either case, the deadline is April 15.

You may buy the stamp at a local post office and place it on your own self-addressed envelope. Send to: Customer-Affixed Envelopes, World Stamp Expo '89 Stamp, Postmaster, New York, NY l0l99-9991. No remittance is required. The Postal Service encourages collectors to use this method and gives these requests preferential treatment.

If you prefer to have the Postal Service affix the stamp, send a self-addressed envelope and personal check or money order for 25 cents per stamp to: World Stamp Expo '89 Stamp, Postmaster, New York, NY 10199-9992.

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The Postal Service is basing its l0th annual spring philatelic promotion on a special edition of the recently issued booklet that features five historic paddle-wheel steamboats. The promotion is designed to increase public awareness of stamps and to encourage stamp collecting as a hobby.

The new offer includes the pane of five 25-cent steamboat stamps, a corresponding Commemorative Stamp Club album page with protective mount, and four 9- by-12-inch steamboat lithographs based on Currier and Ives originals.

The package costs $3. It is available only by mail and only through June 30. Collectors can pick up a self-mailer in local post offices. Collectors unable to secure an order form may request one from the U.S. Postal Service, Washington, DC 20265.

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In 1963, the East African nation of Kenya gained its independence from Great Britain. Part of its Silver Jubilee celebration was the issuance of a set of five stamps honoring the festive occasion.

During the past quarter of a century, Kenya has made significant progress in social, cultural, political and economic areas. The new stamps are a reflection of peace and stability.

The 1-shilling stamp shows the flag of Kenya. The independence celebration featured a special event at Jamhuri Stadium, where the Union Jack was lowered and the black, red and green flag of the new state was dedicated.

The 3-shilling depicts a woman picking coffee. Kenya's economy is primarily agricultural, and depends on crops such as coffee and tea. Coffee accounts for about 25 percent of Kenya's exports.

The 5-shilling features the proposed headquarters of the Kenya Posts & Telecommunications Corp., a 32-story building that is expected to become a landmark of Nairobi, the capital.

The 7-shilling illustrates the Airbus A310-300, one of Kenya's largest planes. It makes domestic flights between Mombasa and Nairobi, and serves such international destinations as Paris, Athens, Frankfurt, Zurich, Rome and London.

The highest value is the 10-shilling, which is a philatelic salute to a new railway engine recently put into service. The Kenya Railways currently operates between Nairobi and Mombasa.

Each stamp in the series bears the special Silver Jubilee emblem.