BOSTON (AP) – A coffee retailer’s advertising campaign on Boston taxis is making some people do a double take when they see the cabs whizzing around the city with a cup of coffee perched precariously on the roof.

The ad campaign, a creation of Clear Channel Taxi Media, is a Starbucks Corp. cup magnetically attached to the roofs of about 100 city cabs. It is the first advertisement of its kind in the nation.

“It’s pretty ingenious,” said Larry Meister, vice president of the Independent Taxi Owners Association.

“People will pull up to cabs driving 55 miles per hour and start beeping and pointing to the roof.”

The ad is a departure from the city’s normally conservative taxi advertising policies. The Boston Police Department’s licensing division in recent years has rejected proposals for wraparound advertisements on taxis as well as promotions on wheels.

“Frankly, this one was so creative we decided to let them do it for a limited period of time,” licensing director Mark Cohen said. “We thought we’d loosen up and see what the response is.”

The rooftop Starbucks ad was offered to a select number of cabs from a few companies, a Clear Channel executive said. “It creates a little buzz and excitement,” said Michael MacDonald, a regional vice president for the company. “It makes people look twice.”