The billboards are eye-catching and funny. The product has a proven, even ancient, track record. Millions of consumers are already steadfastly loyal. And the market includes potentially millions more.

"We need to talk," say the plain white letters on a stark, black background. The message is signed: "God."

This particular sign on Erdman Avenue in southeast Baltimore recently replaced another from the same author. That one admonished passing motorists: "Keep using my name in vain and I'll make rush hour longer."

The signs, which also have appeared in Norfolk and may grace bus shelters in Washington this fall, are part of a national public service campaign by the outdoor advertising industry, which has pledged to temporarily display 10,000 such signs across the country.

The chuckle-inducing signs, which are a set of 18 one-liners supposedly composed by God, have struck a generally responsive chord in these days of distressing post-mortems on school violence and contentious debate over gun control and religion's role in public life.

"I just think it's a good reminder for people," said Sandy Naimaster, the receptionist at Main Steel Polishing, which sits next to the Erdman Avenue billboard on a bleak strip of highway studded with auto parts shops, an emissions testing station and a go-go dancing bar.

"If our country in general goes back to the basic Ten Commandments," added the Edgemere, Md., resident, "then we're all better off."

Michael Henrich, Main Steel's plant manager, thinks the signs are "pretty cool." But the Baltimore resident said they were "pretty shocking at first . . . considering that some of the signs around here had the 'Hooters' girls on them."

Gardner King, general manager of Adams Outdoor Advertising in Norfolk, said his firm garnered plaudits after posting the signs in 100 locations for two months this spring.

"I've had some beautiful letters from people," King said. "They say, 'Please consider putting it up again' or 'It makes me feel wonderful.' "

The origins of the so-called God Speaks campaign lie in Fort Lauderdale, Fla., where an individual walked into The Smith Agency advertising firm last summer and paid $150,000 for the firm to design a campaign to remind people of God.

The person, who still insists on anonymity, "wanted to reach people who used to go to church and for some reason don't go anymore, which is a good-sized group," recalled Smith Vice President Charlie Robb.

The firm thought up the one-line, nondenominational messages. "The idea was that the call to action was going to be in the individual's head," Robb said. "You get a chuckle out of it, but then you think about it."

The messages began running in September in Fort Lauderdale, drawing widespread media attention. Eventually, they caught the attention of the Washington-based Outdoor Advertising Association, which represents 900 advertising companies specializing in billboards, bus shelters and other public spaces.

In January, the association asked its members if they were interested in donating space and materials to run the "God" signs as a public service. Though the group had never chosen a religious topic for such campaigns, "the overwhelming majority said yes," said OAA communications director Sheila Hayes.

"I don't want to sound hokey, but more and more, the response we get from members and the public . . . is that it's time for messages like this," she said. "People are saying the messages are refreshing. They want to see something that gets them talking to their spouses, their kids, their co-workers. I've had people reference Littleton as another example of why we need messages like this." Littleton, Colo., is where the Columbine High School massacre occurred in April.

The Smith Agency donated its original creative work to the campaign, Hayes said. And the participating firms, which cover 200 markets in 40 states, donated materials to print the signs. In March, they began posting them as space became available.

But in some places, including metropolitan Washington, God's message has been delayed by the feast of good times. The area's galloping economy has meant big budgets for promos, which have left no unused advertising space for God.

"Right now, this market is running so strong we don't have the space," said Don Scherer, president of the Washington division of Eller Media, the Phoenix-based firm that already posted 50 signs around Baltimore.

But Scherer, whose offices are in Cottage City, Md., said he'd already ordered the "God" material for billboards in suburban Virginia and Maryland and bus shelters in Washington and hoped space would open for them in September or October.

If they all go up, he added, they will represent "in the range of $20,000 of free media space--and God doesn't ask for an agency discount."

Hayes estimated that if all 10,000 promised displays are posted, the national campaign will represent $15 million in donated advertising. But as with most public service efforts, the industry expects it will earn goodwill and attention. Not only do "God" messages fill space that would otherwise be blank, they also elicit media stories, such as this one.

"It's really a wonderful way for us to show the beauty of our medium," said Norfolk advertising executive King.

Last month, The Smith Agency took a first prize in the industry's annual OBIE Award competition for the "God Speaks" signs. "I don't think I've been involved in anything that's caught on like this campaign," said Vice President Robb. "We thought it would get some controversy, but it didn't."

The anonymous donor is also happy, he added. "You spend $150,000 on a campaign and get about $15 million in media coverage. That's a pretty good return on an investment."

But while the signs are amusing, and for many people thought-provoking, not everyone is convinced they will have much of an impact.

In another rough patch of Baltimore, Eller Media recently refreshed one message from God. The old one--"I love you . . . I love you . . . I love you"--was replaced with "Do you know where you're going?"

Which is a pretty pertinent message because the sign, perched above Three Brothers convenience store on Frederick Street, happens to face Mount Olivet Cemetery.

Inside Three Brothers, owner John Rothenhoefer said none of his customers has mentioned the sign and even he didn't remember its wording. "To be truthful about it, I looked at it, but I can't tell you what it said."

As for the neighborhood, he added, "They need God. I can tell you that. It is full of dope, dope and more dope. . . . People in this neighborhood are basically okay, but they don't have nothing to look forward to and they don't have no direction.

"Whether a sign'll do it? No, I don't think a sign'll do it."

A national public service campaign is displaying messages signed by "God" on billboards and bus shelters in various cities. Among the messages from "God":

* Don't make me come down there

* I don't question your existence

* I can think of ten things that are carved in stone

* What part of 'Thou Shalt Not . . .' didn't you understand?

* You think it's hot here?

* C'mon over and bring the kids

* Loved the wedding, invite me to the marriage

* That 'Love Thy Neighbor' thing? I meant it

* Will the road you're on get you to my place?

* Follow me

* Need directions?

* Tell the kids I love them

* Need a marriage counselor? I'm available

* Have you read my number 1 bestseller? There will be a test.

CAPTION: A sign in Baltimore carries one of the messages that are part of a national public service billboard campaign to raise people's consciousness about God. A person who insisted on anonymity paid for the ad campaign.