MISTAKEN IDENTITIES : What You See Is What You Get--Or Is It? Guess Again.

Apart from my wistful notion that there are really only 3,000 people in the world who matter and everyone else is an extra, there are these numbers, obsolete even as I write them: 31.3 million people live in California, 3.6 million in L.A.

Now it’s all very laudably PC to go on and on about getting to know people instead of judging them from an instant’s contact. But what if an instant is all you have? How do you come to know 3.6 million people? Three thousand? The new neighbor who knocks at your door during Letterman and asks to use the phone?

We have to rely on some gut-level truth-in-human-advertising just to navigate the day. Survival doesn’t depend on whether the guys in the Bartles & Jaymes ad are really Bartles and Jaymes, but it may hinge on a cop being a cop and not Kenneth Bianchi with a phony badge . . . on the man in the camouflage jacket being in the emergency room for treatment and not revenge . . . on the guy in the parking lot with something shiny in his hand being a UNICEF volunteer and not a carjacker.

A ski mask in Big Bear in January means one thing; a ski mask in the Bank of America in August probably means something else altogether. You’d be a fool not to think so. But as long as people are going to leap to conclusions, how far do you want them to go?

Some people choose to do their own advertising.

Up in Sonoma--population less than 1% black--an African-American software exec named Antoine Bigirimana ponied up $1,400 for a full-page ad in the local paper. It bore his face, mugshot-style, and the phrase “I Am Not A Crook.” Since he moved there in 1987, he has been ticketed for a broken car headlight and for not having a bike license, wrongfully arrested for stealing a bike and stopped as he left his office late one night. His ad asked his neighbors: “Was I being treated differently because I was black?”

Other people get their advertising done for them.

In Bakersfield, $40 buys 15 seconds of cable TV time every hour for a week to show the dad or mom who’s behind in child support. It’s supposed to embarrass parents into paying up, so people won’t stop them in the market and scold: “Why, Mr. Ralston--buying raspberries and Johnnie Walker Black, when I heard on the TV that your kids haven’t seen a penny from you since we invaded Grenada? For shame.”

I get unsolicited data thrown in my face all the time. People wear T-shirts that force on me the knowledge of where they vacation (“My dad went to Aruba and all I got was this lousy T-shirt”), what they did on vacation (“Hackensack is for lovers”), their reproductive intimacies (“Baby in the oven”) and what they think of themselves (“Damn, I’m good”).

What I want is an attitude reader to get beyond appearances. The uses would be, oh, endless. It could, for example, help you size up those two cops who’ve pulled you over. What’s going on behind their bad-ass sunglasses?

The first cop is fighting with his ex-wife, who has custody of their kids, so don’t mess with him today. He’s riding with a new partner--though why she thinks she can cut it in this man’s department he doesn’t know.

The second cop just re-read the motto on the door of the police car and thinks, “To protect and serve”--sure, why not? She turned down an invitation to the Rodney King video highlights party, too.

The street person approaching you--is he one of the deserving poor or a bum who would mug you for your shoelaces?

He lost his job under Reaganomics, is not armed and will spend every dime you give him on simple, nourishing food, honest.

And what about the insufferably snotty salesgirl--sorry, sales associate--who’s zipping up the dress you’re trying on?

She would rather be working at the Guerlain boutique with her girlfriend, is doing this only to get through school and can’t believe a woman your age actually intends to go out in public wearing that.

Come to think of it, maybe I’d rather not know.