PORTLAND – The new Nordstrom Rack store is in South Portland, but its presence was evident in recent weeks on the streets of Portland.

A mobile billboard operated by a marketing company based in Pennsylvania rolled repeatedly around the city to announce the arrival of the store.

But billboards, including those on wheels, have been banned in Maine for 30 years — the last one was knocked down in 1984.

A rolling billboard is essentially a flatbed truck with a billboard, roughly 8 feet by 12 feet, on the bed. It can go anywhere crowds gather — sporting events, conventions, beaches on hot summer days — or it can simply circle through a city repeatedly.

The owner of the rolling billboard that was in Portland, Do it Outdoors, even suggests on its website that it could be run in front of a competitor’s place of business for some in-your-face marketing.

Ted Talbot, a spokesman for the Maine Department of Transportation, said rolling billboards are illegal because, just like stationary billboards, their only purpose is to display advertising.

If a vehicle serves a legitimate transportation purpose, it can carry advertising. Beer delivery trucks are plastered with ads for various brews, and Metro buses are literally wrapped in ads.

But don’t expect a state trooper to pull over the next rolling billboard you see and write out a ticket, Talbot said.

First, it’s not a ticketable offense. And second, the Department of Transportation has only one enforcement officer, who is often enforcing other rules, such as making sure political signs don’t violate billboard laws or obscure highway signs.

If someone complains about a rolling billboard, Talbot said, the department will likely call the owner’s office and tell them about Maine’s law.

If there’s a second complaint, the department’s lawyers will draft a stern letter, he said, asking the company to cease and desist.

After that, it’s a trip to court to get an injunction to stop the mobile billboard, Talbot said.

Finally, it’s up to the court to enforce the law, probably with fines, if the company fails to heed the injunction.

Talbot said he could find only one letter to a mobile billboard operator in his agency’s files over the past five years.

He said that concerned a jeweler’s promotion for a big sale in 2008 that involved about a half-dozen mobile billboards rolling around the state. By the time the letter was sent, he said, the sale was over.

That appears likely to be the case with the Nordstrom Rack ads.

Regis Maher, president of York, Pa.-based Do it Outdoors advertising, said the contract for the Nordstrom ad ran out Sunday and the mobile billboard was back in Pennsylvania by Tuesday.

Maher said neither Nordstrom Rack nor New England Development, which owns the Maine Crossing shopping center, where the store is located, hired his company. He would not say who did.

He also declined to say how much it costs to hire his billboard trucks.

Maher said he has been sending Do it Outdoors’ trucks to Maine for years, and he and his staff check local ordinances before sending out a rolling billboard. He said he wasn’t sure whether Maine’s laws were researched.

Some towns and cities have banned mobile billboards, saying they create a traffic hazard and eat up parking space when the trucks pull to the side of the road. Maher said he and the Outdoor Advertising Association of America have fought some of those bans and have occasionally argued successfully that carrying advertising is the same as carrying a product.

Maher said he doesn’t expect to send any more trucks to Maine. He didn’t sound too happy about it.

“We try to abide by every local law and ordinance,” he said, “but it’s a freedom of speech issue, in my eyes.”

Edward D. Murphy can be contacted at 791-6465 or at emurphy@mainetoday.com