Miami-Dade County is asking politely: Please don’t smoke in the park. After all, the air is fresh, kids are running and jumping — and panting from all the exercise — and, most important, secondhand smoke can be a killer.

Since last summer, the county has been putting up signs in heavily used parks, those where lots of kids congregate for baseball games, soccer matches, family picnics and any other fun.

The county is taking the pretty-please approach because, thanks to a state law passed in 1985, that’s all it can do. The Florida Clean Indoor Air Act prohibits counties from banning smoking outdoors. Therefore, the county’s request that people not smoke in its parks is a policy, not law.

No one will be fined, cited or arrested for lighting up. So the policy’s effectiveness depends on smokers’ basic sense of civic duty and accountability.

Here’s why they should comply: According to the American Heart Association, being subjected to secondhand smoke for as few as 20 minutes increases one’s risk of developing coronary disease. Hang around smokers every day, and the risk can increase by up to 30 percent. In addition, the 2010 Surgeon General’s report found that there is no safe level of secondhand smoke, which sends more than 70 chemicals that can cause cancer wafting into a nonsmoker’s lungs.

Why impose that on anyone, especially children?

Throw in, too, poor modeling — given what’s known, smoking’s not the best behavior to which to expose kids, now is it?

All this should be more than enough incentive to curb the craving for a while. If anyone should ask you to extinguish the smoke, just do it. It’s the right thing.

One potential danger for children that state law now does allow is carrying a gun in a park. We don’t condone it and neither do most counties nor cities, but the gun lobby has its way in Tallahassee. South Florida counties might want to use the no-smoking pretty-please model and post signs about guns. It’s worth making that request, too — politely.