Ottawa (AFP) - A man prosecuted for selling marijuana has asked Canada's high court to weigh in on whether posting a "No Cops" sign should have warded off police scrutiny of his storefront.

The defendant operated a small shop selling drug paraphernalia in Abbotsford, British Columbia. He posted a sign at the front door warning police they were not allowed on the premises without a warrant, according to court documents.

The man's lawyer also wrote to the market town's police chief advising officials they are not welcome at the store.

Undercover police ignored the warnings and went in to purchase marijuana from the store owner, who was then charged with trafficking of an illicit drug.

At trial the evidence was thrown out on the basis that the sting amounted to an unlawful search. But the man's acquittal was overturned on appeal.

The British Columbia Court of Appeal ruled that the store is a public place and so police may enter to investigate criminal activities.

"An objectively reasonable expectation of privacy in a retail store could not be achieved simply by posting a sign excluding law enforcement officers," Justice Nicole Garson said in the decision.

The Supreme Court of Canada is now considering whether to hear the case.