Dressing for the campaign trail has its own rules: Nothing tricky, nothing too interesting, nothing that distracts from the message. Legibility is key.

I was watching some newswoman hold forth on a topic of national importance on TV the other night when I realised I'd completely quit listening to what she was saying, so riveted was my attention on her necklace. Occupational hazard, I guess. She was wearing a thickish gold chain with some sort of cylindrical doohickey suspended from it but, even with HDTV, I couldn't tell quite what it was or what it was made of.

Here's another place where men have a definite (if arguably slight) advantage over women. You never lose track of what Brian Williams or Chris Matthews or Morley Safer is saying because you're so caught up in trying to figure out what he's wearing around his neck: It's always a tie.

Women have so many more choices — but, if they're on TV to analyse the situation on the ground in Fallujah, or opine on the Fed's latest rate tweak, or run for president, they want you to be paying attention to that, not their fascinating accessories.

I suspect this explains the recent ascendancy of "power pearls," the single strands of gumball-sized Tahitian or South Sea pearls that first came to prominence when Nancy Pelosi wore a multicolored string of them on election night last year, and that have been seen circling the throats of other women who wield or aspire to power. (Hillary Clinton wore a strand for one of the debates.)

Pearls — soft, glowing, innocent — might seem a counterintuitive choice for a politician. But there's plenty of historical precedent. A new book for beading enthusiasts, "Create Jewelry: Pearls," notes that Queen Elizabeth I was so fond of them that she was sometimes called "the Pearl Queen." She especially liked wearing gowns embroidered with pearls, and kept a fleet of embroiderers busy removing them from one dress so they could be used to decorate another. That's pearl power for you.

The knockoff necklaces that online jewellers have been selling as "Pelosi pearls" are power pearls of a different sort. They aren't Jackie Kennedy's double-strand fakes, meant to look elegant and grown-up, or Barbara Bush's respectable, grandmotherly triple strand, or Mrs. Jay Gould's my-husband-is-richer-than-anybody rope of Oriental pearls that were said to be worth half a mil — in 1880 dollars. They aren't your sweet-girl-graduate string of graduated pearls, or your opera-length strand of perfectly matched pearls the color of homogenised milk.

They're big. They're often colorful: A necklace can be black or gray or golden or peach or several different shades of gold and cream. They look expensive, not that you can tell whether they're real on TV. Jewellers have estimated the price of Pelosi's at anywhere from $12,000 to $80,000.

You can find copies online in the $3,000-to-$6,000 range, but you can also find plausible fakes made from ground seashells on eBay for opening bids as low as 99 cents. But what makes them so useful to a woman who needs to make a point on television isn't that they're pretty or pricey-looking, it's that they're instantly legible.

Even on an old-fashioned low-def TV, one look tells you the woman on the screen is wearing pearls, so now you can pay attention to what she's saying.

It's something even a woman as accomplished as Clinton or Pelosi might've learned from Marge Simpson, who's never without a choker of jawbreaker-sized beads. They're the perfect cartoon accessory: simple, quick to draw, immediately recognisable as the archetypal necklace. Like a cartoon character, a woman who wants to be a successful talking head on TV can't afford to distract her audience with fussy, hard-to-interpret details. Hence all the tailored jackets, the classic shirts and the jewel-necked shells, styles that are themselves as stripped-down and stereotypical as cartoons.

At least women have license to pay attention to what they wear and how it affects people. Men are somehow still not supposed to care, which is why the idea of Naomi Wolf advising Al Gore to wear earth tones to look more grounded was so entertaining. American men have at one time or another bought bales of Hawaiian shirts, plaid pants, zoot suits, ruffled tuxedo shirts, falling-down-gigantic blue jeans, you name it, and still there's this ridiculous expectation that real men don't even notice what they have on.

Nearly every time Barack Obama showed up on TV this summer he was wearing the same thing: a suit (usually gray, I think) and a crisp white shirt with a spread collar, collar button undone, no tie. The suit suggested a proper regard for appearances, a recognition that people look for a certain gravitas in their president — maybe more so if he's only 45.

The starched shirt had dignity but, open-necked and tieless, it also looked relaxed, open, accessible. The suit-shirt-no-tie combo made him look new, not like your typical pol.

It gave him a consistent visual identity, and it made the rest of the male candidates, flip-flopping back and forth willy-nilly from T-shirts and jeans to polo shirts and khakis to the whole buttoned-up suit-and-tie rig, look as if they couldn't decide who to be.

Normal people do that all the time, of course, but a candidate is more like a box of cereal: If it doesn't look the same every time you see it on the shelf, how do you know it's really Wheaties?