PHILADELPHIA (Reuters) - Philadelphia is taking on businesses that blanket its neighborhoods with illegal paper and plastic signs by using automated phone calls to disrupt the operations of people who post them along with contact numbers.

“It’s as plain as that,” said Philadelphia Streets Commissioner David Perri. “We hook them up to robo-calls so all their voicemails get filled up.”

City officials are recording phone numbers on the advertisements, which hype everything from cash for junk cars to fixer upper homes. The numbers are put into a database that makes “robo-calls” about city programs every 15 minutes.

The often brightly colored advertisements, known as bandit signs, have long irritated civic leaders who see them as a blight. The city has struggled to eliminate them by levying fines for each sign and encouraging civic groups to tear them down.

The illegal ads are visible by the dozen on city streets, particularly in low-income neighborhoods. They advertise bootlegged products such as counterfeit DVDs and T-shirts, illegal nightclubs, and other enterprises.

City officials have said enforcement has been hampered by lack of manpower and because the businesses are hard to track.

Perri said some of the businesses, especially those buying junk cars, rely on disposable cell phones and meet customers in public places.

Perri said the robo-calls, which began about a year ago, have reduced illegal ads by about two-thirds.

Officials in Oakland Park, Florida began using robo-calls in 2012 to combat similar illegal ads