Outdoor advertising is a good way to get out the message. And a nonprofit nondenominational Christian ministry has it pretty much figured out.

California-based Gospel Spots likes billboards, though it delivers its message of redemption via radio and TV, too. The organization was founded by Bob Anthony Fogal in 1998 and mostly relies on donations, he said.

Fogal, who has spent years in media broadcasting, coordinates with billboard and broadcast companies to place his advertisements. In 1982, Fogal founded the K-Love Christian Radio Network. In 1995, he started the Air One Radio Network. Today, he devotes most of his time to Gospel Spots, he said.

"Eleven years ago, I left (commercial media) to pursue using mass media to communicate the gospel," he said.

The evangelical nonprofit has arranged to have its outdoor ads mounted in many states, including South Carolina. Recently, one of its billboards could be seen near Columbia.

A highlight of Gospel Spots ministry so far was a 30-second spot it ran in Portland, Ore., during the 2005 Superbowl, Fogal said. It cost $30,000 and was viewed by 1.4 million people.

"If you have the money, you can reach a lot of people," he said.

Advertising managers pay close attention to something called "return on investment," or ROI, in an attempt to determine whether their ads are effective.

ROI is hard to quantify in the best of circumstances, even when physical products are being sold, according to marketing experts. It might register as a jump in sales; it might register as a change in perception.

Nevertheless, if a billboard advertises a new lawn mower, and subsequent sales of that mower increase at nearby home improvement stores, it's fair to assume that the billboard helped, or possibly helped, or at least didn't hurt.

But what about metaphysical products? What about the marketing of ideas, such as salvation?

It is practically impossible to count the number of people who decide to go to church after seeing a billboard promoting religion, unless the billboard was purchased by a specific church and members of its staff are interviewing visitors and new members. It's even harder to know how many viewers of religious advertising abide by the message and achieve its promise.

A recent billboard advertisement purchased by the American Humanists Association and the Secular Humanists of the Lowcountry, which is mounted along U.S. Interstate 26 in North Charleston, has prompted an explicit reaction.

The humanist billboard provoked criticism from a few Christians who wrote letters to the editor of The Post and Courier and e-mails to this reporter saying they were insulted by the advertisement's message.

Fogal, who was familiar with the larger advertising campaign launched nationally by humanist organizations, called their messages an attack on Christians.

"We don't attack atheists," he said.

The humanist billboard read: "Don't believe in God? You're not alone."

Herb Silverman, vice president of the Secular Humanists of the Lowcountry, said he wasn't surprised to know that the billboard was controversial. But it also served its intended purpose, he said.

"The billboard has had an effect, with many inquiries and several new SHL members," he wrote in an e-mail. "Our webmaster said we are getting a lot more hits."

But quantifying the impact of a billboard ad isn't important to Gospel Spots, Fogal said. Nor is using the advertisements to raise money for the nonprofit.

"Our call to action, if you will, is a heart action," he said, and the message on the billboards is simple and direct: "Repent and believe."

There is no request for money, he said. There is no big branding effort. There is only one purpose.

"Our charge is to go into all the world and preach the gospel," he said.