IT ISN'T LIKELY that anyone will slip a secret mark onto Tom Broad's latest stamp.

The Chevy Chase artist has drawn a turn-of-the-century milk wagon so simply for a new 5-cent stamp that it would be difficult to hide anything on it.

Broad's last effort was a $1 stamp honoring Jewish immigrant Bernard Revel, onto which engraver Kenneth Kipperman of Silver Spring etched a tiny Star of David.

The design for Broad's milkwagon stamp, released last week by the Postal Service, should cause few worries at the Bureau of Engraving and Printing, where the star's discovery caused a furor. The stark simplicity of Broad's gray stamp and the purple 17 1/2-cent stamp to be issued with it in Indianapolis September 25 will have stamp traditionalists -- who favor hand-engraving -- cheering.

The two stamps are part of the Postal Service's highly popular transporation series, produced in coils of 100 to 3,000. Although intended for bulk mailers, their crisp designs have given them a strong following among collectors.

Both the milkwagon and racing- car stamps will be issued at the Indypex Stamp Show, a convenience for first-day collectors, who need a minimum of 22 cents postage on any first-day cover. It's also a blessing for the Postal Service's first-day cancelling center in Merrifield, which has been working double shifts to keep up with more than 100 new stamps issued this year.

By paying 23 cents each, collectors can get two new stamps on a single cover and the workers will cut in half the number of first-day envelopes they have to run through their cancelling machines.

McLean artist Lou Nolan's 17 1/2-cent stamp seems ideal for the Hoosiers. It features the Marmon Wasp that Ray Harroun drove around a course known as "the brickyard" at an average of 74.602 mph to win the first Indianapolis 500 in 1911.

The 17 1/2-cent rate is for mailers who qualify for discounts by presorting their letters using the Postal Service's nine-digit zip codes. The pre-cancelled version of the stamp is also one of the few in the transportation series to have two colors. "Zip+4 Presort" will be printed in red, the car in purple.

The design of last year's 22-cent Duke Ellington commemorative, a pensive profile of the pianist in white tie and tails, was all too familiar to photographer Katsuji Abe of Tokyo. He went to the U.S. Embassy complaining that the Postal Service had stolen the design from a photograph he took in 1966.

Last week, the service announced Abe was right and said it was paying him $500 and issuing a press release on the "distinguished Japanese photographer" to settle the dispute. The fee was the same that the service pays for "reference material" used in designing stamps, said Frank Thomas, a Postal Service spokesman.

The service said both it and Doubleday & Co., publisher of "Music Is My Mistress," an Ellington autobiography that contained the photo, believed it to be in the public domain -- until Abe saw the stamp.

The Postal Service has announced that another of Lou Nolan's stamps, a 22-cent commemorative celebrating the 100th anniversary of the accounting profession, will be released September 21 during the opening of the American Institute of Certified Public Accountants' five-day convention in New York. That means that the ceremonies, unlike most new stamp events, will be closed to the public.

First-day cancellations will be available until October 21 for collectors who send envelopes with the stamp affixed to Customer- Affixed Envelopes, CPA Stamps, Postmaster, New York NY 10001-9991. The Postal Service will affix stamps to as many as 50 envelopes at a price of 22 cents each at CPA Stamps, Postmaster, New York NY 10001-9992.

Collectors seeking the milkwagon and racing-car stamps are cautioned that the latter may not be available at many post offices and may have to be obtained from postal philatelic centers. Individuals sending the new stamps can obtain cancellations from Customer-Affixed Envelopes, Milkwagon/Racing Car Stamp, Postmaster, Indianapolis IN 46206-9991. The Postal Service will affix both stamps to envelopes for 23 cents at Milkwagon/Racing Car Stamps, Postmaster, Indianapolis IN 46206-9992. The deadline is October 25.

Bill McAllister is a member of The Post's national staff.