WASHINGTON  An unusual holiday message began appearing this week in the nation’s capital on the sides of buses and trains.

“No god? ... No problem!” reads the advertisement featuring the smiling faces of people wearing Santa Claus hats. “Be good for goodness’ sake.”

Over the next two weeks, 270 of the ads will go up on city buses and trains in the Washington area as part of the holiday kickoff to campaigns sponsored by secular groups in cities around the country and abroad. If last year was any indication, the signs are likely to spark a theological war of words.

“We don’t intend to rain on anyone’s parade, but secular people celebrate the holidays, too, and we’re just trying to reach out to our people,” said Roy Speckhardt, the executive director of the American Humanist Association. “To the degree that we are reaching out to the godly, it’s just to say that you can be good without god. So their atheist neighbor down the street shouldn’t be vilified as though he is immoral.”