As regular visitors to this space well know, I think vanity license plates are marvelous. For cleverness and brevity, how can you beat FATN40, or FOXY1, or 4HIRE? Don't try. You can't.

But some vanity plate lovers are forever trying to stray to the dark side of decency. Motor vehicle departments all over the country are flooded each year by proposals that would make Hugh Hefner blush -- not to mention your maiden uncle in the next lane.

Usually, DMVs reject anything that's the slightest bit doubtful in terms of taste. But there's a new way to play Beat The Censors. It's called The Rear-View Mirror Method.

You order a plate that looks as innocuous as rice pudding when you read it head-on -- for example, XES. But if you read that tag in a rear-view mirror, it becomes SEX. Needless to say, there are much steamier (and seamier) possibilities.

The Rear-View Mirror Method was working just beautifully for a man out in Leesburg. But last month, Cathy Mitchell blew the whistle on him.

Cathy had been trying to figure out the guy's plate for ages. Then, one day, she happened to read it in her rear-view mirror. Since this is a family newspaper, I can't publish the rear-view version of the plate. Let's just say that it contains six letters. The first two, as you view it in the mirror, are AW. The last four complete one of the most enduring epithets of them all.

Cathy says she's no prude. But she's also the mother of three kids, ages 12, 10 and 2, "and I didn't want them asking me, 'Hey, Mommy, what does s--- mean?' " So Cathy went to the Virginia DMV office in Leesburg and complained.

"It was actually kind of funny," Cathy said. "All the clerks came over and gathered around to have a look. They love it when somebody slips one through the system."

But the system didn't stay slipped for long. In accordance with standard procedure, the DMV contacted the owner of AW----, took it away from him and replaced it with another plate that's not as offensive.

In the case of AW----, it's pretty clear that the Virginia DMV did the right thing. And I'd say the same in any case of Rear-Viewism where a patently offensive word appeared.

But there are many judgment calls that are much, much closer. How do DMVs approach the question of what's permissible and what isn't?

In Richmond, the DMV rules out "swear words, references to religious deities and references to ethnic groups," said Paula Kripaitis-Neely, the agency's director of public information.

Virginia will also try to negotiate with a vanity plate owner to see if he'll accept a less offensive version of a tag. For example, Paula recalled a man who was issued HITLER one year. After negotiations, he agreed to accept ADOLF instead.

Steve Horwitz, Paula's counterpart with the Maryland Motor Vehicle Administration, said that his department will sometimes allow a motorist to keep a controversial tag because of the motorist's explanation.

Last year, for instance, a motorist was allowed to keep LSD, despite many complaints. Why? Because LSD were his initials.

However, Maryland disallowed 6UL DV8 (sexual deviate) just a few days ago, even though that's a perfectly legitimate term that's found in respected medical dictionaries.

"You have to look at these things carefully and with a jaundiced view," explained Steve, to researcher Wendy Melillo. "People would like to slip one by us."

Nowhere do they try to slip 'em by more often than in America's car capital, California. And nowhere does a state meet the attempts with as many bodies, or as much research.

Jay Martin, manager of the unit that approves vanity tags for the California DMV, said her staff consists of 35 people. They're from every conceivable ethnic and national background (to ward off foreign terms). And if they're in doubt, they can call on a library of slang dictionaries, a bank of computers, even the foreign language faculty at Sacramento State College.

California being what it is, Jay has a large supply of kooky stories. My favorite was the guy who applied for 4NIC8 (fornicate).

Jay's staff denied the application, of course, and the motorist complained -- in highly imaginative fashion.

"He said the request was for his brother, Nic, who had an eight-cylinder vehicle," Jay recalled. "We told him if Nic had a 6-cylinder vehicle, he could have the plate."

So California is safe from that rather remarkable twister of the truth, and Virginia must do without AW----. Could this mean that vanity tag seekers will now become as pure as the driven snow?

Paula Kripaitis-Neely would bet against it. As she noted, "we reject about 15,000 combinations a year." Obviously, the wise guys are still trying, and they probably always will.