San Francisco - Armies of would-be political candidates knocked on doors throughout the US Friday.

But with only four days before the historic elections, instead of shaking hands, holding babies, giving overused stump speeches and asking citizens for their vote, they had a much simpler request - "Trick or treat?" - and demanded nothing more than a piece of chocolate or a sweet or two.

In a time-honoured tradition that occurs every four years when Halloween falls just before election day, the most popular costumes this year were not dragons, dinosaurs, or young teenage nurses in inappropriately sexy costumers.

Instead, it was the political contenders of the day who ruled the ghostly night - John McCain, Barack Obama, and of course Sarah Palin, who also was often depicted in inappropriately sexy costumes.

Another hot favourite was the lipstick-wearing pig - a satirical reference to Obama's campaign remark about McCain's economic policies that was misconstrued as an insult aimed at the Republican vice presidential candidate from Alaska after she had described herself as a pitbull wearing lipstick.

The intensity of this year's campaign has been a bonanza for the makers of political costumes, even amidst the economic doldrums, said Mike Danford, who owns and operates a Halloween costume store in San Francisco.

"I've never seen anything like it," he said. "Obama and McCain are obviously popular but Sarah Palin costumers are getting snapped up like they're going out of fashion - which personally I hope they are."

At a Halloween store in nearby Oakland, owner Greg Wills said he had run out of Sarah Palin masks.

"I kept calling my supplier every day but the answer was that they couldn't make them fast enough," he explained.

Asked whether this insatiable demand reflected support or disdain for the Republican vice presidential candidate, Willis said that he always sells more costumes of the candidate who eventually loses.

"Just because you wear a mask of someone doesn't mean you are going to vote for them," he said. "In fact it means that you probably want to make fun of them."

Sometimes people cross the line, however.

In the avowedly liberal and strongly gay enclave of West Hollywood, Secret Service agents investigated a house where someone had hung a mannequin of Palin as part of an elaborate Halloween display.

The display also featured a hellish portrayal of McCain - he was showing surrounded by flames coming from the house's chimney. Though the Secret Service concluded that the display was not sinister, local Republicans called it a hate crime since it targeted the candidates based on their political affiliation.

"Had this stupid act been done to Senator (Barack) Obama, there would appropriately have been a national outcry," said county supervisor Mike Antonovich.

Homeowner Chad Morissette insisted it was the candidate's policies that were scary, not his effigies. "If it's a political statement, it's that (McCain's and Palin's) politics are scary to us," Morrisette told The Los Angeles Times. "This is our palette and this is our venue of expression."

In nearby Redondo Beach, a right-wing voter was also expressing herself. She displayed a lynched effigy of Obama from her balcony - complete with a meat cleaver slashing his throat, his red necktie configured into a noose and his suit covered with blood. She was eventually persuaded to take down the effigy after a visit from McCain's local campaign organizer.

Whatever their political opinions, there's little doubt that Americans' growing desire for a brief escape from reality is fuelling a massive Halloween industry.

An estimated 51.8 million adults will dress up to celebrate Halloween this year, according to the National Retail Federation, which estimates that a total of 5.77 billion dollars will be spent nationwide this year on the distractions of Halloween costumes and merchandise.

This was especially true in the battleground state of Ohio, one store owner told his local paper, the Freemont News Messenger.

"People get so tired of hearing all of the negative campaigning that by the time Halloween arrives, they are ready to party and have some fun," Greg Kearns, owner of the Costume Holiday House, was quoted as saying.

"Halloween happens to fall during a time when things have become very serious and tense with friends and colleagues arguing politics. Dressing up gives people a chance to put their differences aside for a night, forget their problems and let their hair down," he said. dpa