To thousands of L.A. drivers it's a godsend. To transportation authorities it's a potentially dangerous counterfeit. But to conceptual artist Richard Ankrom the doctored sign over the Harbor Freeway is simply his most ambitious work to date. Ankrom, 46, was miffed at missing the northbound exit for Interstate 5, which, curiously, the sign failed to mention. "I wasn't going to deal with the bureaucracy," he says. Last August Ankrom scaled the sign and added an I-5 logo and the word "North" while cars whizzed by 20 feet below. "It was incredibly surreal," he says.

It was also illegal—but the California Department of Transportation didn't discover the forgery until a pal of Ankrom's tattled to the press last month. (The artist had hoped to unveil a video of his "performance" at a gallery this summer.) Though Caltrans spokeswoman Deborah Harris complains that Ankrom "put himself in danger, as well as motorists underneath the sign," she says the agency won't pursue charges against Ankrom, adding, "He obviously put a lot of time and energy" into the project.

In fact it took two years to plan, a week to assemble in his loft and 20 minutes to install. Ankrom found the specs on government Web sites and purchased the materials for $350. To pass as a road worker, he bought a hard hat and an orange vest, created a fake work order and had his shoulder-length locks shorn. "I told the barber, 'Make me look like Johnny Lunchbox,'" he says.

Ankrom, whose oeuvre also includes neon stun guns and swords studded with roses, pays the bills by crafting signs for local stores. He didn't make a dime on his freeway frolic, but that's okay: With an average of 161,500 viewers a day, he can't beat the exposure.