All the world’s a billboard.

In cities across America, there seems to be hardly a square foot of space left that doesn’t beckon commercial enterprises to “place your ad here” for a fee. There are ads all over city buses and taxis, and ads that cover professional athletes from the caps on their heads to the sneakers on their feet. Half the sports arenas and entertainment complexes in the country now carry the ridiculous-sounding names of their corporate sponsors.

During the World Series, TV viewers were forced to watch ads for products and new shows on the Fox channel on an irritating electronic billboard behind the catcher that changed with every at bat.

And the trend appears to be getting worse all the time as hungry pitchmen increasingly look to gobble up every inch of our public property, too. The city of St. Charles, Mo., for instance, voted in September to rent ad space on its garbage trucks to help shore up its depleted municipal coffers. San Diego is considering letting General Motors slap ads on all its lifeguard towers in exchange for 35 new vehicles.

In New York, there are vans that cruise the streets at night to beam ads onto tall buildings. And Biggs, Calif., is actually discussing an offer from the California Milk Processor Board to change its name to Got Milk?, Calif., in exchange for a “meaningful contribution” to the town.

Our kids, for that matter, are nothing less than walking billboards for Gap, Abercrombie & Fitch, Tommy Hilfiger, Old Navy and countless other clothing companies.

So should anyone really be surprised that a Charlotte, N.C., company is offering new police cars for $1 each to cash-strapped municipalities across the country, with free replacement every three years, provided the communities agree to the NASCAR-style advertising that’s printed all over the cruisers?

The oddest part of the story is not that someone was clever enough to come up with such a scheme, but that 20 cities have already signed up for the rent-a-cop-car offer and more than 200 others have inquired about the deal.

“We’re trying to save the taxpayers money,” said a New Jersey mayor who’s thinking about getting 18 ad-plastered patrol cars from the company.

Considering how many Maine cities and towns are struggling to make ends meet, and that we’re among the most heavily taxed populations in the country, is it too far-fetched to think that some of our most desperate municipal leaders might one day find this deal too good to pass up?

“Uh-oh, I think there’s a cop car following us.”

“No sweat, man, it’s just a Domino’s Pizza car.”

“Maybe, but this one’s got blue lights on top.”

The more I think about this curious new money-saving measure, the more pitiful it seems. Is it possible that we might see a cop car going by that proclaims on its doors: “City of Bangor. Home of the Whopper”?

Could we really expect our Maine police departments to maintain law and order when their cruisers are rolling through town with ads for “Betty Crocker” or the “Pillsbury Dough Boy” splashed across their hoods and rear ends?

It’s easy to understand why many police chiefs in the country, budget-constrained or not, have scoffed at the idea of using their patrol cars as rolling billboards, and wonder about the poor cop who gets stuck driving a car that advertises a feminine hygiene product or Depends adult diapers.

After all, advertising a company like Dunkin’ Donuts on a police cruiser might work as an inside joke, but a Super Poligrip ad would almost certainly take the teeth right out of your average nightly drug bust.

And I cannot imagine getting a ticket from an officer driving a car that has “Dude, you’re getting a Dell” printed on its doors. It’s just too hilarious to even contemplate without laughing.

A cruiser pitching tough-sounding products like Raid, or Bounty, the Quicker Picker-Upper, is one thing, but I doubt there’s a perp on the planet who would feel the least bit intimidated by an approaching patrol car that advertised Huggies or Toys R Us.

Some social-policy experts are advising that communities with money troubles might be better off to wait out the bad times rather than hastily turn their police forces into modern-day versions of the Keystone Kops. Once a town starts selling off its pride by hawking Oscar Mayer Wieners, they say, its dignity may be lost forever.

Just ask the good folks of Got Milk?, Calif.