(FORTUNE Magazine) – MARK WADSWORTH JUST chuckles when he thinks of it. Still tooling around on Mars with slowly dying batteries, the twin rovers Spirit and Opportunity--which began sending pictures of the Red Planet's relentless bleakness to Earth early last year--are inhabited by what Wadsworth calls "tiny Martians." There are 36 of them up there, and they're all smaller than the period at the end of this sentence, he says.

Wadsworth, a microcircuitry designer by profession, is also an artist of sorts. And he isn't kidding about the Martians. Etched onto the rovers' camera chips--specialized photosensitive chips known as charge-coupled devices (CCDs) and akin to chips in household digital cameras--are microscopic images of the Warner Bros. cartoon character Marvin the Martian. There are two of them per chip, staring at each other with malevolence.

When Wadsworth and longtime collaborator Tom Elliott designed these sophisticated silicon eyeballs for the multitude of cameras that the two rovers carry, they "signed" their handiwork with these heads-only versions of Marvin, which now have actually become extraterrestrials. The engineers, whose printed names appear under each set of helmeted Marvins, had heated "discussions" when working on the chip together at the Jet Propulsion Laboratory in Pasadena. "That's why we made the dueling heads," says Wadsworth, who now runs Tangent Technologies, a specialty CCD company in Monrovia, Calif.

Like a blade of grass pushing up through blacktop, art--or at least personal expression--is irrepressible, even in the microscopic confines of silicon chips. Too small to be seen without a microscope, and often in violation of managerial prohibitions, images have been appearing on chips since the 1970s.

Call it chip graffiti. And look at it now, because it's dying out.

There has always been art of an engineering sort in chips--the microcircuitry can even look a little like a busy Mondrian. But for a rebellious cadre of chip designers who could not let their creations exist without some signature, some sign that even the most arcane technology springs from human imagination, the empty spaces on their chips have served as silicon microcanvases. The world's collection of chips, in everything from nuclear submarines to video accelerator cards, harbors a hidden gallery of the smallest art that ever was. The entire known global portfolio of these works probably could fit inside this O.

Chip graffiti might have remained an insider's art form had microscopist Michael Davidson of Florida State University not been so small-minded. In the early 1990s Davidson was, in his words, "trying to advance chip photography as an art form." He was spending a lot of time cracking open chip casings and peering inside with microscopes. In 1993, while he was examining one of those chips, a microprocessor known as the MIPS 4400, his socks got knocked off.

"I saw something that looked different from most other things on the chip," Davidson recalls. He cranked up the magnification and looked again. "I saw this Waldo thing," recalls Davidson, referring to the character in the Where's Waldo? cartoon books. At first Davidson thought the microscopic Waldo served as a kind of anti-copying feature, but a few months later, on the same chip, he found a teeny tiny Daffy Duck. Now the hunt was on.

"As I looked at more chips, I saw more graffiti," Davidson says. "I started seeing things out in the gutters, in pad rings, and things in areas that normally don't have any [circuitry]." By 1998 he had found a dozen examples. He referred to them collectively as a "Silicon Zoo" and posted them on a website that was featured by Wired.com. "That's when a lot of chip engineers started sending me designs," Davidson says. His Silicon Zoo is now populated by more than 300 works of micrograffiti.

Many engineers merely printed their initials on their chips, as though they were signing a painting. Some etched corners of their chips with humorous word graffiti, such as this takeoff on a famous bumper sticker: IF YOU CAN READ THIS, YOU ARE WAY TOO CLOSE. But much of the chip art is in the form of images, among them cheetahs, buffalo, rabbits, sailboats, trains, space vehicles, Groucho Marx glasses-and-mustache masks, and even seductresses and con artists. One chip designer doodled a "can-o-worms" on the edge of a chip to represent the glitches that arose during the chip's development. This one is reminiscent of the unauthorized and often humorous, lascivious, or subversive doodlings that medieval scribes sometimes added to the lavish embellishments for pages of the ancient works they were copying.

Davidson's online gallery of chip art (microscope.fsu.edu/creatures/) is the most extensive one out there, and the quality of his images reflects the countless hours he has invested in finding just the right angles, lighting, and imaging tools for revealing the minuscule art. Perhaps the only other sizable gallery of chip art on the planet resides on the website of the "reverse engineering" firm Chipworks in Ottawa. Chipworks' analysts still periodically run across new examples as they tease apart the details of chips for such uses as intellectual property lawsuits and testing companies' product claims. The Silicon Art Gallery is the most frequently visited part of company's website (www.chiworks.com/ gallery/ gallery_home.asp), says Chipworks president Terry Ludlow.

But the pace of micrograffiti discovery at Chipworks has been waning, Ludlow says. Diminutive to begin with, chip graffiti really may be disappearing.

Practitioners and observers of the art blame the downturn on technical and sociological changes in the chipmaking culture. For one thing, says Dan Zuras, a retired chip designer who tries fairly successfully to not consult, there's less personal incentive to sign chips now than in the past. It used to be that one individual or a small team would spend years designing and drawing circuit patterns that would be deposited in miniature onto silicon wafers. "If you invest that much of yourself into something, you just want to sign it," says Zuras, whose first micrograffiti works were in the form of a poisonous snake, an adder, which he and co-workers put onto math-processing chips they worked on at Hewlett-Packard.

Today chip design is most often done by large collaborations using automated design tools. It still takes expertise and knowledge, but Zuras says the process doesn't readily instill the sense of ownership that makes you want to sign the product.

Another damper on chip graffiti comes from the chain of command. "In the early days, our boss was into this, so we did not have any trouble," says Zuras. "But as chip projects got larger, more bureaucratic, and driven and controlled by software, the managers become more separated from the designers. They became afraid of [chip graffiti], because it might break something."

And sometimes it did.

Wadsworth recalls an instance in the late 1980s when he was working for Texas Instruments. A fellow designer there who was working on a chip slated for a missile guidance system incorporated an image of the Three Stooges. As the design moved forward in the development process, quality assurance inspectors kept seeing apparent flaws, which were, as Wadsworth remembers it, the "tiny frayed hairs of Larry." That caused expensive delays in the chip's production. "The fellow that did that lost his job," Wadsworth says.

Not that such things stopped designers like Wadsworth or Willy McAllister, a former colleague of Zuras's who now develops DNA microarray chips--for biomedical analysis and diagnostic uses--for Agilent Technologies. "We didn't do what we were told; we did what we wanted to," says McAllister, whose chip graffiti portfolio also includes cheetahs, panthers, and leopards. "It's my chip, damn it, and I'm going to do what I want," he says.

McAllister says he wants to put graffiti into his new microarray chips, but he concedes that today's chip designers may have to find other ways of making their personal marks. "You'll never find graffiti on an Intel chip," he says, noting the vast stakes. To managers at the Intels of the world, he says, anything that is surprising, uncontrolled, or unauthorized in the chipmaking process is playing with a kind of fire that could lead to catastrophic technological, commercial, and financial failures.

To the imp in each of us, it may seem a shame that micrograffiti is fading. But then McAllister and his fellow artists never intended their "in silico" art to find its way into the public eye. They had expected that the signs of humanity they were leaving would remain forever hidden by sheer tininess and the tough plastic, metal, or ceramic casings that enclose the chips. Never has art been purer. ■