Stamps of approval.

As an investment, rare stamps can outstrip the S&P 500. But many CEO philatelists are passionate about what others see only as gummed paper.

When John Sununu fell from grace as White House chief-of-staff in 1991, one of the contributing causes was his use of presidential transportation to attend a stamp auction in New York. It is only at such moments that most of the non-stam collecting public becomes aware of the hobby. Serious adult stamp collectors, o philatelists, tend to keep low profiles. Usually they become known to the general media only after their deaths, when the rarities in their collections are auctioned for large sums.

"Rare stamps often are purchased not for exhibition, but simply for possession, says stamp auctioneer Walter J. Mader. "Many of the greatest collections are rarely seen."

Among business leaders, today's better-known collectors include Thurston Twigg-Smith of Honolulu's Persis Corp. (newspapers and real estate); Jack Rosenthal of Casper, WY's Clear Channel Radio; and Bruce McNall, not only owner of the Los Angeles Kings hockey team, but also the majority stockholder of one of the nation's leading philatelic businesses--Los Angeles' Superior Stamp and Coin Company.

Some collectors began the hobby early and have found it increasingly rewarding. "I started when I was 11 years old," says McNall's friend, Jerry H. Buss, owner of the L.A. Lakers. "As I matured, the relaxation I could gain by spending a fe hours with my stamps became increasingly important to me. By the time my business holdings reached the one-half billion mark, the solace and comfort I received from philately became one of the most important things in my life."

Ounce for ounce, a rare postage stamp can be the most valuable object in the world. The greatest of philately's rarities, the unique British Guiana 1 cent magenta stamp of 1856, is a one-inch square piece of paper that weighs a tiny fraction of an ounce. At the stamp's current valuation in excess of $1 million, neither gold, nor platinum, nor diamonds, nor van Gogh's "Sunflowers" comes close in value per weight.

Irwin Weinberg is fascinated by the British Guiana stamp, not least by the fact that it can be bought and sold. "Think how many of the world's treasures are no for sale," he told The New Yorker magazine in 1970. "The Mona Lisa. The Sistine Chapel."

Weinberg, a well-known dealer in Wilkes-Barre, PA, bought the British Guiana fo $280,000 in a 1970 auction. At the time, this was a record price in the world o philately, and Weinberg and his stamp received international publicity. Ten years later, Weinberg and his syndicate of rare stamp investors quietly sold th British Guiana to a collector for $935,000, including a 10 percent auctioneer's fee.

Stamps can be a sound investment, but only if they are rare and in the finest condition possible. Condition, especially, is key, though there are exceptions to this rule, including the trimmed, shabby British Guiana itself.

To the uninformed eye, all stamps look much the same. Knowing the difference marks the true philatelist--or the successful dealer. "Knowledge is power," Weinberg says. "You can make lots of money if you know that one stamp that look like another is really more valuable." In a recent auction by the noted firm Ivy, Shreve & Mader, a fairly common early U.S. commemorative stamp--the 5 cent blue Pocahontas issue of 1907--went for $1,430 because of its vivid color, perfect centering, and superb condition. An ordinary example of the same stamp is readily available for less than $100.

Errors are valuable, too. One stamp in this category is probably the most famou and coveted issue of all: the 1918 red and blue 24 cent U.S. airmail stamp with the "upside-down," or inverted, bioplane. One hundred of these errors, a complete sheet of stamps, were created when a printer's mistake sent one half-printed sheet through the press for the second color upside down. Though the U.S. Post Office carefully inspected all of the stamps before offering them to the public, that sheet slipped through and was purchased at a Washington pos office for $24 by someone who immediately recognized its value. The buyer quickly sold the entire sheet for $15,000, a considerable sum in 1918. Today, better-quality single copies will bring $100,000 and up when they appear at stamp auctions.

However, one copy of the inverted "Flying" Jenny (as the stamp is called) probably will not bring a full price when it next appears for sale. A couple of years ago, its proud owner was looking through his album in his library. When h turned the page, the Jenny flew out of its mount and onto the carpet, unnoticed by the collector. And unnoticed by his maid, too, when she vacuumed the carpet shortly afterward. Fortunately, the collector discovered his stamp's absence before the vacuum cleaner's bag was emptied, and there the stamp was found, considerably the worse for wear.

Despite their historic and geographic significance, stamps essentially are bits of gummed paper, separated from one another by perforations, printed by various methods in various colors. In the early days of collecting, over a century ago, enthusiasts usually tore them from envelopes and pasted them in albums. When th British Guiana stamp was found by a 13-year-old English schoolboy in 1873, it was still attached to an envelope--a cover to collectors--with a postmark and other information modern-day philatelists would prize. But the boy removed the stamp so he could add it to his collection.

Initially, the idea was to get a sample of as many different varieties as possible--though one English enthusiast papered the walls of a room with used copies of Britain's (and the world's) first stamp, the one penny black Victoria of 1840. In the century after 1840, stamp collecting evolved into philately, th serious study and classification of stamps and their use. The second half of that century was the age of such famous collectors as King George V of Great Britain and U.S. President Franklin D. Roosevelt. Some of the prominent America philatelists of that era include well-known CEOs such as Alfred E. Lichtenstein of Ciba-Geigy, Josiah K. Lilly Jr. of Eli Lilly, and Stephen Bechtel of Bechtel Corp.

Most of today's philatelists collect new issues of nations or brightly colored "topical" stamps (international issues showing birds, locomotives, famous people, etc.). But with some notable exceptions, the famous rarities that make news are mid-19th century stamps, those often beautifully engraved issues that appeared long before most people thought of collecting them.

Auctions are an important source of rare stamps for most collectors, here and abroad. In addition to Ivy, Shreve & Mader, the leading auction firms with offices in New York are H.R. Harmer, Robert A. Siegel, and Christie's; they issue catalogs with good illustrations and informative comments on each lot.

"To make sure you get what you thought you bought, use a well-known dealer," says Irwin Weinberg.

But whatever the value of your philatelic holdings, if they don't also give you "relaxation, solace, and comfort," you've missed the best part of the hobby. Says Walter Mader: "Stamp collecting is therapeutic--a person can lose himself.