Holiday hooliganism in the US is no longer limited to thieves running off with baby Jesus from a nativity scene or vandals throwing eggs at mangers.

Atheist decorations also have become a target for destruction after their addition to some public forums in recent years as a counter-argument to menorahs and nativity scenes, a Wisconsin-based secularist group has said.

"It's not unusual at all to run into these heavy-handed tactics," said Annie Laurie Gaylor of the Freedom From Religion Foundation (FFRF) last Friday.

Of a dozen FFRF displays erected in winter 2012, five were stolen or vandalised, Gaylor said. In 2013, 14 displays were put up, and two were vandalised.

An atheist banner in a park of the Chicago suburb of Arlington Heights vandalised twice, in 2013 and 2014, and the Chicago FFRF chapter is offering a $2,000 reward to find the culprit.

The now-repaired banner asks "Are you good without God? Millions are."

Last year in Pitman, New Jersey, someone tried to set an atheist billboard on fire.

Gaylor said the banners and lighted "A" for atheist signs are in response to religious displays, which the foundation said should not be in public places such as parks or government buildings.

One of the foundation's displays is a "Bill of Rights" nativity scene, to commemorate the Dec. 15 ratification of the first 10 amendments of the US Constitution.

"It's the founding fathers gazing adoringly at the Bill of Rights in a crib. James Madison is on bended knee," said Gaylor.

One out of five US adults do not identify with a specific religion, according to a 2012 Pew Research Center study, the highest percentage ever for that group in Pew polling.

"There has to be room at the inn for non-believers," Gaylor said. "Many more people are offended when they encounter religion at the seat of their government."

Tom Brejcha, a lawyer for the Chicago-based Thomas More Society, which has fought to protect religious displays in public forums, said vandalism of both atheist and religious displays is wrong. But he thinks the atheist displays are an attempt to discourage free speech.

"I think it's really an attempt to try to get people angry and make it divisive so the public officials involved will suppress people expressing themselves on something that's important to them," said Brejcha.