SEATTLE — Putting up a billboard saying “Imagine No Religion” at the base of Capitol Hill, in the heart of not-too-churchgoing Seattle, is a bit like preaching to the choir. So to speak.

Mike Christensen knows this. But he’s OK with it.

When he paid for the sign about a month ago in support of the Freedom From Religion Foundation, his goal never was to change people’s minds. It was to get people thinking and talking. And maybe, just maybe, get a few more members for the foundation, which fights for the separation of church and state.

The 14-foot-by-48-foot billboard, on Denny Way near Stewart Street, has brought in five new members and about 20 prospective ones, according to the Wisconsin-based foundation.

“I like the phrase ‘Imagine No Religion’ because it doesn’t make a judgment,” said Christensen, 28, a software engineer from Redmond. “It provokes thought.”

Christensen, an atheist, joined the Freedom From Religion Foundation several years ago because he thought the Bush administration was getting too involved in religion.

A widespread campaign

The 30-year-old foundation started its billboard campaign last year.

So far, it’s put up about a dozen signs in seven or so cities, including Atlanta and Columbus, Ohio. The group had a billboard reading “Keep Religion Out of Politics” about six blocks from the Democratic National Convention in Denver, and plans to have a similar mobile billboard at the Republican National Convention in St. Paul, Minn.

The billboards are “to remind people that we’re here too,” said Annie Laurie Gaylor, the foundation’s co-president and co-founder. “If we don’t make our presence known, as the nonreligious, then religion just wins by default.”

Gary Randall, president of the Faith and Freedom Network, a lobbying group for the state’s conservative Christian community, supports the foundation’s right to express its views through the billboard.

But “I think there’s a relentless challenge to anything Christian on the part of the minority who are atheistic and agnostic,” he said, citing, for example, legal challenges over religion in public schools.

Billboard companies in some cities have refused to put up the foundation’s signs, and the group has gotten hate mail from people in other cities where billboards have appeared, Gaylor said.

The Seattle billboard, though, has resulted in support not surprising, given that in Washington, 23 percent of residents are unaffiliated with a religious tradition.

Dan O’Connell, a high-tech professional in Seattle, joined the foundation after seeing the billboard on Denny and e-mailed friends about it.

He thought the billboard was “extremely brave, given our current climate.”

Steve Kaattari, a marine-science professor from Williamsburg, Va., was visiting his son when he saw the billboard. He’s now scouting sites for a billboard near his home.

“It just knocked my socks off,” he said. “You’d never see something like this in southeast Virginia.”

As of last week, the billboard was covered with a black sheet. That’s because a new sign, from another company, is being put into that space, said Chris Artman, manager of the Seattle office of Clear Channel Outdoor, which owns the billboard.

Christensen said that’s fine, given that the billboard company had let his sign stay up for many days after the period he had paid for had passed. Christensen had paid for his sign to be up for only a month, from about early July to early August.

Good timing?

It may be an opportune time to spread the message of non-faith. A recent spate of books such as “The God Delusion” by Richard Dawkins and “God Is Not Great: How Religion Poisons Everything” by Christopher Hitchens have made best-seller lists.

A survey released earlier this year by the Pew Forum on Religion and Public Life found that more adults said they were atheists or agnostics than were raised that way.

But Gaylor believes there’s a paradox in that “the danger to the separation of church and state has never been greater.”

She points to the foundation’s loss last year in a Supreme Court decision saying taxpayers lacked standing to challenge the White House’s faith-based initiatives.

Charles Haynes, senior scholar with the Freedom Forum’s First Amendment Center, said the intent of the First Amendment was not to ban religion from the public square but to keep government from establishing a state religion.

On the other hand, “it’s hard for anyone to argue that religion is disadvantaged in the United States where religion is everywhere participating in public life, politics,” he said.

Some who saw the Seattle billboard suggested putting one up on the Eastside. But Christensen said he’s just sponsoring the one.

“The point of the billboard is to inspire one person to one thing,” he said.

“I’m not going to change anyone’s mind from a three-word billboard.”