(FORTUNE Magazine) – If imitation is truly the sincerest form of flattery, then Jeff Manning must be feeling pretty good about himself.

Manning is executive director of the California Milk Processor Board, the trade group behind the ubiquitous "Got milk?" ad campaign. Since debuting in California in 1993 and going national in 1995, "Got milk?" has inspired dozens of copycat campaigns--some authorized, some not--ranging from a Combat insecticide ad with a "Got death?" caption to an adult bookstore with a "Got porn?" sign in the window. Manning says that he's even seen panhandlers holding "Got work?" and "Got change?" signs.

Considering the extent to which "Got milk?" has permeated the fabric of contemporary pop culture, Manning's a pretty humble guy. "We just created what we thought was a pretty good ad campaign," he says. "Soon it became clear that something magical was happening, and then of course we fed the fire. But we didn't start off with the goal of becoming part of America's vernacular."

Neither did Amy Heinemann, director of marketing for the International Dairy Foods Association, which administers another widely copied milk-promotion effort, the "Where's your mustache?" ad series. "We knew it was going to be popular," says Heinemann, "but the degree to which it's become a pop icon has taken us a bit by surprise." Heinemann, like Manning, says she's seen scores of derivative ads, most of which she regards as free promotion. "If it's in good taste and doesn't compete with us, then it doesn't bother us," she says, although she and Manning both report having fired off the occasional cease-and-desist letter. (They decline to specify which parodies have gone too far.)

If you're surprised to hear that "Got milk?" and "Where's your mustache?" are two separate initiatives, you're not alone. There was no link between them until a month or so ago, when milk mustache ads began carrying a "Got milk?" tag line, but Manning and Heinemann agree that the two campaigns long ago became one in the public mind. Indeed, many of the copycat ads blend the campaigns: A Disney ad for George of the Jungle showed star Brendan Fraser with a white mustache and a "Got coconut milk?" caption, and a terrific HBO ad for The Larry Sanders Show depicted a mustachioed Garry Shandling and a "Got milk of magnesia?" tag line.

But some derivatives are decidedly less inspired. One of the more curious examples was recently launched by Pocket Books for its Archway Paperbacks and Minstrel Books imprints, which cater to children and teens. The campaign centers on a display rack featuring a photo of a smiling boy, whose upper lip and cheeks are adorned with a bizarre-looking "book mustache"--a strip of paper with some random text that appears to have been torn out of a book. A caption, printed in an unmistakably "Got milk?"-esque typeface, reads, "Got books?"

Uh, got any better ideas than that? "What we're trying to get across is that books are wholesome, a lot like milk," explains Kathryn Briggs Gordon, Pocket's associate marketing director. "And not only are books good for you, but they're also fun." It's not clear why having a strip of paper glued to one's face would be "fun," but let's suppose for a moment that it is. Now imagine thousands of fun-loving kids seeing Pocket's "Got books?" display rack, taking Pocket titles off the shelf, and tearing out pages to turn into book mustaches. Got a good returns policy?

Such concerns notwithstanding, Pocket appears to have done "Got books?" by the book. Unlike many of the imitators, Pocket sought permission from Manning's and Heinemann's offices, both of which gave their approval. "The ones considerate enough to ask are usually doing a tasteful campaign," says Heinemann. "In this case, it's not a competitive product, and it doesn't disparage milk in any way, so if they can use our campaign to further a good, educational message, we're happy to help." As for the book mustache gimmick, Heinemann is more circumspect. "Um, I thought it was clever," she says, clearly trying to be gentle. "Obviously, it's odd to see the words on the lip like that, but I think it's very attention getting."

Very diplomatically put. This attention-getting factor, which is common to most of the milk copycats, obscures a larger question: Why are so many marketers playing off the milk ads instead of coming up with their own ideas? "In some cases, I think it reflects poorly on the ad agency, and maybe on the advertiser," Manning says. "If an agency came to me with a derivative of someone else's advertising, I'd probably fire them." Which may explain those out-of-work panhandlers he's been seeing lately.

PAUL LUKAS, author of Inconspicuous Consumption, obsesses over the details of consumer culture so you don't have to.