After years of discussion, commercial advertising could be coming soon to municipal buildings, libraries, recreation centers, and even trash trucks in Philadelphia - potentially netting the city tens of millions of dollars.

At least 12 "major players" in the advertising business so far have answered the city's call for proposals to manage the sale and placement of ads on municipal property, Managing Director Richard Negrin said.

He said it would be hard to know how much money the city could make "until you see the scope of the proposals." The deadline to respond is Thursday.

SEPTA, which has had ads on buses, trains, and stations for years, recently renewed a contract with Titan Outdoor L.L.C. that guarantees the transit authority $150 million over seven years.

"It's going to be at least in the millions of dollars," Negrin said. "Certainly every dollar helps."

That was the point City Council President Darrell L. Clarke made when he first floated the idea of selling ads on city property more than two years ago, before he became president.

"We're encouraged that the city has taken the first step," Clarke said this week. He said his goal was to find new ways to generate revenue "so . . . our first response to fiscal issues won't be to raise people's taxes."

Ads could appear on city property by the end of the year, Negrin said.

Critics see billboards and other signs as a blight on the cityscape, and have been fighting for years to limit their spread.

Mary Tracy, executive director of Scenic Philadelphia and perhaps the most vocal foe of billboards in the city, called the plan to place ads on municipal property "unbelievable."

"We're really turning on its head all the great progress we've made in curtailing advertising and commercialism," she said. "It's very disheartening to live in a city that so little values its aesthetic treasures that it would sell them off."

The city's request for proposals lists 58 of the 134 rec centers and 45 of 54 libraries, including the Central Library, as potential sites for advertising. The Municipal Services Building and the One Parkway building, both of which are next to LOVE Park and the Benjamin Franklin Parkway, also are included.

Tracy said library and rec-center advocates were extremely "protective" of their buildings, and noted that advertising is supposed to be banned from the Parkway.

Negrin said the city would be "incredibly sensitive to honoring our historic buildings," as well as cautious when it comes to ad content around libraries and rec centers.

He said a committee that would review proposals from advertising firms and make recommendations to Mayor Nutter would have "maximum flexibility to say yes or no" to individual ideas.

But he said the city "didn't want to limit folks" in the initial phases.

There are restrictions. The city won't accept ads for alcohol, tobacco or firearms. Nor would sexually explicit or political ads be accepted.

The city said more than 4,000 city vehicles were eligible for wrap or roof advertising, but Health Department cars would not accept ads for food and drinks, pharmaceuticals, or medical services.

The city also doesn't want traditional billboards. But "wall wraps," digital signs, and even projections would be considered.

Council previously approved a wall wrap for the Electric Factory building at Seventh and Callowhill Streets. But community groups opposed the plan and Nutter vetoed it in 2012.

Council would have to approve a multi- year contract with a vendor for advertising but already has passed necessary zoning permission.

Negrin noted that the NHL set up a well-received projection display at the Clothespin sculpture across from City Hall to promote the Winter Classic several years ago.

As for the Municipal Services Building and One Parkway, Negrin said he liked the kind of mobile monitors and elevator wraps often seen in hotels and office buildings.

"We're an office building like any other," said Negrin, whose office is in the Municipal Services Building. "I'd also like to see what's the thing that nobody's done yet."

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