PONOKA, Alta. - A judge in Alberta has convicted a man of stunting after he was pulled over by police for driving his car with a sign with an expletive aimed at former prime minister Stephen Harper.

Robert Wells of Edmonton was driving home from British Columbia when he was pulled over in August 2015 by an RCMP officer near Ponoka, Alta., and told to remove the sign.

He refused, saying it was a political statement and he had a right to have it in his window.

Judge B.D. Rosborough wrote in his ruling that the handmade "F--k Harper" sign didn't amount to stunting itself, stating that it didn't amount to a dangerous trick or manoeuvre.

But Rosborough said he believed testimony that Wells was deliberately slowing down and cutting in front of traffic on Highway 2 so that people would see his sign.

The judge said Wells was interfering with the orderly progress of other vehicles on the highway, which he said met the criteria for stunting.

"Display of a sign in the rear window of a vehicle was hardly a notable or impressive act of skill or daring," Wells wrote in his ruling. "Likewise, it could not amount to an exciting or dangerous trick or manoeuvre," he continued.

"On the evidence that I do accept, I am satisfied that Wells was intentionally interfering with other traffic in order to advertise his 'anti-Harper' sentiment."

Wells, who represented himself when the case was heard earlier this year, said he knew he had to challenge the ticket because it suppressed his right to freedom of expression.

The Crown argued there are other ways to express oneself and a busy highway is not the right place for such political discourse.

Wells was also pulled over by Edmonton police 15 years ago, after he displayed a bumper sticker with the same expletive aimed at former premier Ralph Klein to protest his government's push for private health care.

He said he wasn't charged because police determined he wasn't doing anything illegal.