Officials say Philadelphia's municipal buildings, libraries, recreation centers and even vehicles such as trash trucks could soon bear commercial advertising that could raise tens of millions of dollars.

Managing Director Richard Negrin told The Philadelphia Inquirer that the city's call for proposals to manage the sale and placement of ads on municipal properties has drawn a response from what he called at least a dozen "major players" in the advertising business.

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

The Southeastern Pennsylvania Transportation Authority has displayed ads on city buses, trains and stations for years.

Critics, however, have fought for years to limit signs, calling them a blight on the cityscape. Mary Tracy, executive director of Scenic Philadelphia, called the plan "unbelievable."