The call came around midnight the night before the men's snowboard halfpipe final at the 2002 Winter Olympics in Salt Lake City. The caller, a representative from the United States Olympic Committee, explained to Bob Klein a problem involving Danny Kass, Klein's client at the time and a medal favorite in the pipe final: Kass would not be permitted to compete, the official warned, unless Quiksilver removed a poster from its storefront in Park City, Utah, with a message wishing him good luck at the Games.

Klein, an agent for Octagon, quickly phoned Quiksilver, one of Kass' sponsors, and made sure someone pulled down the poster. Hours later, Kass won a silver medal; today he laughs about the flap. But for Klein it seemed like a close call.

Kass' crime? He had unwittingly run afoul of Rule 41 in the International Olympic Committee's charter, the so-called "Blackout Rule," which bans competitors, coaches, trainers and officials participating in the Olympics from using their name or image for advertising during the Games. Only those whose sponsors pony up a substantial sum to be an official Olympic sponsor receive an exemption from the IOC's executive board.

With the Winter Games under way in Vancouver this week, officials have again cracked down on marketing in an effort to bar brands from piggybacking on the popularity of the Olympics. Although most brands comply, some run roughshod over the IOC's rules out of ignorance. And others flirt with gray areas in the rulebook, resorting to guerilla or ambush marketing, a kind of gamesmanship that acts as a sideshow to the athletic spectacle.

"Sponsors try to get as creative as possible walking that fine line," said Brian Gainor, founder of Partnership Activation Inc., a consulting company offering marketing strategies to sports business professionals. "Everyone's just trying to capitalize on buzz."

Last month, Target unveiled a series of billboard panels in Times Square featuring Shaun White, defending gold-medal winner in men's snowboard halfpipe and a Target-sponsored athlete. White appeared in animated form, along with scenes of animals and other characters acting out winter activities, several of which happen to be Olympic events.

But by the time the Games began on Friday, Target had altered the billboard: White had faded to black, replaced by a silhouette, and a message -- "Gone to Vancouver."

"Our goal with the Times Square billboards was to show our support and excitement for Shaun's return to the Games," Troy Michels of Target Lifestyle Marketing said via e-mail. "We're really happy with both the pre- and post-blackout artwork and have been receiving a lot of positive response. We worked hard to respect the rules outlined for the competing athletes."

But other brands have wound up in the IOC's crosshairs for borderline ambush tactics.

Sandwich-maker Subway stirred up controversy last month with a TV commercial showing Olympic swimming star Michael Phelps. In the ad, Phelps uses Subway's sandwiches as fuel to swim across a map that reads C-A-N, to "get to where the action is this winter," an allusion to the Vancouver Games.

Subway sponsors Phelps, but not the Olympic Games. Meanwhile, McDonald's, an official sponsor of the USOC, complained about the commercial. The USOC owns exclusive rights to market Olympic marks, the Olympic rings, Olympic Games and the U.S. Olympic team. And with no government funding, the USOC relies on corporate support from the likes of McDonald's to fund U.S. Olympians.

"The way we help the Olympic movement is we use the marks to raise revenue for our athletes," Lisa Baird, chief marketing officer for the USOC, said last month. "And when a company crosses that line -- and I'll name Subway as one of those companies that has crossed the line -- it hurts our athletes."

Ambush marketing is not limited to the Olympics, though. During an NFL game in November versus the Dallas Cowboys, Philadelphia Eagles tight end Brent Celek celebrated a touchdown catch by posing in the end zone like Captain Morgan, the pirate pictured on the namesake spiced rum bottle, with his right leg raised and his left hand on his hip. The NFL promptly banned the "Captain Morgan," citing the celebration as an example of ambush marketing on the playing field.

For sports leagues and organizing bodies, controlling ambush tactics can be a game of cat-and-mouse.

"They're about as tough as it comes," Gainor said of the Olympics, but added, "There's so much territory they can't control."

This week Team USA hockey goalie Ryan Miller caught the attention of Olympic officials for painting "Miller Time" on the back of his helmet. The words, evoking the High Life to some, were deemed in violation of Rule 51, which forbids advertising, publicity or propaganda at the Games. As a result, Miller covered the words with a sticker reading U-S-A during an opening round win over Switzerland on Tuesday.

The sizes of logos on skis, snowboards and goggle bands can potentially violate the rules, too. Images on goggles, hats, sunglasses and gloves, for example, can be no larger than 6 square centimeters, roughly the size of a book of matches.

"There are definitely people plotting," Klein said about brands hoping to gain some increased Olympic exposure by pushing the limits. Kass, a founder of Grenade, a glove and apparel company, helped build his brand with guerilla marketing strategies at contests, using blowup dolls, banners, and a grenade stencil and cans of spray paint.

"We tried to own a certain area of the halfpipe with crazy banners and pickets," said Kass, who did not qualify to compete at the Olympics this week, but who will be on hand to root for Grenade riders Louie Vito, Scotty Lago, Greg Bretz, Iouri Podladtchikov and Elena Hight. "A lot of it was about doing something different. We didn't want to be like the next snowboarding company."

But at the 2002 and 2006 Winter Games (where Kass also won silver) the Grenade approach ran into Olympic watchdogs waiting with rolls of black tape. Kass said he managed to wear Grenade-brand gloves, and stickers on his headphones, but officials "attacked" his goggles, covering logos with tape, and made him turn inside-out any clothing that was not part of the Olympic uniform.

Ben Seeley, marketing communication manager for the IOC, said most instances of violations are unintentional. The IOC works with national Olympic committees in advance of the Games to set guidelines for logos.

"Worst-case scenario, you have to tape that logo or mark it," Seeley said.

Still, for shreds accustomed to the somewhat laid-back approach at other large events such as the X Games, the marketing blackout at the Olympics can seem especially harsh. Although athletes and agents sign a contract stipulating they will not resort to guerilla marketing at ESPN's Games, enforcement can be lax, especially if there's no official sponsor in a particular product category.

Ever since Mountain Dew departed as the official beverage sponsor of the X Games to start its own action-sports tour with NBC in 2005, competitors have rocked water bottles with the logos of energy-drink sponsors on camera at the X Games with impunity.

"It's definitely a lot friendlier on products and the industry," Kass said about the X Games compared to the Olympics.

For some shreds at the Olympics, a little exposure can mean the difference between paying the rent and going into debt. Many of Klein's clients are members of the U.S. Snowboard Cross team, a group with no professional tour and scant support from the endemic snowboarding industry.

"I have to say, ethics rule out for me," Klein said about adhering to the rulebook. "But if somebody says, 'We'll give you half-a-million dollars to do the Captain Morgan's kick,' we'd certainly be willing to consider it."