Barker said the display is especially important given that 25 percent of Washington state residents are unaffiliated with religion or do not believe in God. (A recent survey by the Pew Forum on Religion and Public Life found 23 percent of Washingtonians said they were unaffiliated with a religion and 7 percent said they didn't believe in God.)

"It's not that we are trying to coerce anyone; in a way our sign is a signal of protest," Barker said. "If there can be a Nativity scene saying that we are all going to hell if we don't bow down to Jesus, we should be at the table to share our views."

"Most people think December is for Christians and view our signs as an intrusion, when actually it's the other way around," he said. "People have been celebrating the winter solstice long before Christmas. We see Christianity as the intruder, trying to steal the holiday from all of us humans."

"Why believe in a God?" the advertisement asks. "Just be good for goodness sake."