Don't let the 30-foot-high inflated AMERICAN TOURISTER gorilla or the walking, talking GEOFFREY THE TOYS-R-US giraffe fool you. At a Commerce Department exposition called "How Business Makes Its Mark" at the Washington Tourist Information Center this past weekend, trademark officials of well-known companies made their point: Trademarks may be cute, but don't mess with them.

While TONY THE TIGER and the M plain and peanut characters stalked the hall shaking children's hands (and occasionally making them shriek in terror), trademark attorneys, paralegals and communications officers explained why a trademark is more than meets the eye or ear.

"The trademark is used as an adjective, never as a noun, to modify a generic term," said Helen Murphy of M&M/Mars. "The generic term is always ld,10 spelled out in upper-lower case and the trademark is always spelled out in all caps to stand out from the rest of the line."

Thus: "M&M's Plain Chocolate Candies," "M&M's Peanut Chocolate Candies" and "TWIX Twin Cookie Bars" are official. So is the slogan "KEEP ON MOVIN' WITH TWIX ."

"We try to make sure our trademark is used capitalized as an adjective," said James Boudreau of the Coca-Cola Co., which makes either "COCA-COLA " or "Coca-Cola ." "It's hard to describe."

"A trademark is a proper adjective so it should always be followed by a noun," said Linda Cook of Hershey Foods Corp. It should be distinguished with italics, underscoring, quotation marks or all capitals and followed by a circled R. "In this case," Cook said, pointing to one of her company's products, " 'SAN GIORGIO ' is the trademark which should be emphasized and the general word for the product is 'spaghetti.' "

Sometimes trademark grammar contradicts English grammar. The familiar foil-wrapped chocolates are "HERSHEY'S KISSES chocolates." One of them is a "HERSHEY'S KISSES chocolate." You might think this presents a singular problem.

"It doesn't if you use the brand name 'KISSES ' to refer to one or two," said Cook.

Joan Weber of Dart & Kraft Inc., busy handing out free TUPPERWARE gum and candy keepers, agreed. "The trademark is the adjective and it's followed by a noun. Whether it's singular or plural doesn't matter." Irrefutable logic.

Steven M. Getzoff of American Express grabbed a confused reporter's notebook to demonstrate the right way to spell some of his company's trademarks: "GOLD CARD ," "PLATINUM CARD ," "DON'T LEAVE HOME WITHOUT IT ."

"American Express has a very intense internal and external policing policy," he said. "Our presence here today talking to the public is part of our worldwide intellectual properties policing efforts." A trademark, he added, "can't be used in a simple English language way. It has to be used distinctively."

Domino's Pizza Inc. had a dispute with a sugar company over its brand name and isn't allowed to use the word "pizza" as a generic term described by "DOMINO'S" as a trademark. "You never say, 'Get your DOMINO'S pizza,' " said the company's John Hogan. "We have to say, 'Get a pizza from DOMINO'S PIZZA.' You don't want to say, 'Get your DOMINO'S PIZZA pizza.' "

To simplify things, the Commerce Department's Patent and Trademark Office put up signs giving helpful information such as: "A trademark is like an artist's signature on a painting. Think of a trademark as a manufacturer's signature." And: "Trademarks carry U.S. products throughout the world." The COCA-COLA logo, America's commercial/cultural ambassador to the world, illustrated the point nicely. "GENIET COCA-COLA" is a "Trad Mark Regd" in South Africa, and "DRICK COCA-COLA" is a "Reg. Varumarke" in Sweden.

An electronic shell game presented ignorant consumers with much-needed information on the Mennen Co. If the spot under your underarm deodorant cap lit up, revealing a message such as "First Air Freight Shipments of Toiletries" or "First Medicated Foot Powder," you won a key chain or lollipop.

John Casey of ShowAmerica Inc. amused the tots with a robotized HEINZ ketchup bottle. He had a microphone up his sleeve and a control panel in his pocket. "I just left a Colgate pump in Denver," he said. "He was Mr. Pump, I guess. This one is Easy Squeeze because the kids squeeze him and his ketchup comes out and raises his lid."

Casey didn't specify whether it was a COLGATE pump or MR. PUMP or maybe COLGATE PUMP .