A billboard in Costa Mesa, Calif., is getting some attention, but it's certainly not the kind its sponsors were hoping for.

The sign, paid for by atheist group Backyard Skeptics, includes a quote about Christianity attributed to Thomas Jefferson. But further research reveals there's no solid evidence that Jefferson ever uttered or wrote the words, the Orange County Register first reported.

The billboard includes a picture of Jefferson with the quote: "I do not find in Christianity one redeeming feature. It is founded on fables and mythology."

Experts at the Jefferson Library Collection at Monticello are constantly asked about the quote, the Orange County Register reports. Some say the former president wrote the words in a letter to a Dr. Wood, but officials cannot find trace of any correspondence to a person by that name.

Bruce Gleason, a member of the group, told the Orange County Register that he should have done a bit more research before putting the words on the sign. The billboard was unveiled on Wednesday, the newspaper reports. Gleason explained that purpose of this sign and others around the city was to "expunge the myth that this is a Christian nation," as well as to "share the idea that you can be good and do good without a religion or god."

UPDATE: 6:24 p.m. --

Jefferson kept a personal book containing certain verses from the New Testament and the Gospels of Matthew, Mark, Luke and John, the Los Angeles Times points out. He arranged the snippets into a small "scrapbook," which left out mentions of the virgin birth, Jesus' resurrection, and other forms of divinity and miracles. He called it, "The Life and Morals of Jesus of Nazareth," but it later came to be known as the "Jefferson Bible."

The founding father identified himself as a Christian, despite his questions, the Christian Post explains. Scholars have debated the issue, and some have posited that "without acknowledging Jesus' divinity and resurrection, Christianity [is] baseless."

Author Lori Ann Ferrel, who's written about the "Jefferson Bible," told the Los Angeles Times that Jefferson "was more skeptical about religion than the other Founding Fathers."