As the weather warms, the sounds of summer are starting: Birds singing, the ping of baseballs hitting bats, the chatter of children frolicking outdoors - and the roar of dirt bikes and ATVs tearing around city streets and parks.

That last urban bane already has prompted Philadelphia police to issue their annual appeal to citizens: They want fans of four-wheelers and dirtbikes to stay off public property and residents to report scofflaws.

"These vehicles are not legal to drive on the city streets. They are also frequently operated in a reckless manner with disregard for pedestrians and other vehicles. The police department needs your help in preventing and stopping the illegal use of these vehicles," the appeal implores on the department's blog.

So far this year, police have confiscated 36 ATVs and dirt bikes in periodic crackdowns, according to the blog.

While it's illegal to ride ATVs and dirt bikes on city streets and in parks, thousands flout the law and do. Police policy prohibits officers from chasing offenders, but that policy isn't always followed, riders say.

The practice has proven deadly. The Daily News wrote about the problem in 2012, prompting city leaders to toughen penalties against offenders.

Police urge anyone seeing dirt bikers or ATV riders on city streets or parks to call 9-1-1 or (215) 686-TIPS.