Erin Mersino, trial counsel for the nonprofit Thomas More Law Center, which supports “America’s Judeo-Christian heritage and moral values,” said the ordinance in effect bans the expression of ideas in what would traditionally be a public forum — a sidewalk.

“It’s amazing that the government has overreached in this fashion,” she said.

Campbell town attorney Brent Smith said Monday he had not seen the complaint but that the town stood behind the ordinance, citing a federal court of appeals ruling in the case of a Monroe, Wis., pastor who was forced by Madison police to take his anti-gay protest off a Beltline overpass in 2003.

The court ruled that it was the spectacle of the protest, and not the message, that prompted police to remove the pastor.

“We aren’t out on a limb, and we didn’t just manufacture this,” Smith said. “We did look at that ordinance, and we did look at that court decision before we went forward.”

But Bernardo Cueto, one of the attorneys representing Luce and Newman, said that’s a misreading of the appeals court decision, which applied only to the police action. It was only later that Madison banned all signs on highway overpasses.