Three California start-up companies are racing to turn the average person's car into an advertising vehicle. . . .Not everyone is thrilled with this phenomenon. "It's part of ad creep," says Gary Ruskin, head of nonprofit awareness group Commercial Alert. "As ad budgets go up and clutter increases, ad firms are trying to find any innovative way to stick ads in front of our noses."

CBS one night in February turned its popular Monday lineup of four situation comedies into an Elizabeth Taylor sell-a-thon. Taylor was billed as a guest star, and she won the network better-than-usual ratings. In exchange, the four shows, through an interconnected storyline that saw Taylor searching for a black pearl necklace, became a two-hour, unlabeled infomercial. Her new signature odor is called Black Pearls.

So what, says Gil Schwartz, CBS's senior vice president of communications. "Some people have charged that television is commercial," Schwartz says, dripping sarcasm.

"At no time did Elizabeth Taylor touch a bottle of perfume, nor hawk her product. This was in this case a hopefully witty and tongue-in-cheek series of references to what Alfred Hitchcock would call a MacGuffin, a device that moves the plot along.

"To view this as an intrusion into sacred air time by crass commercialism would be at best humorless and at worst glum."

But critics of the trend note that making a joke out of ad creep is the technique's favored form of camouflage.