South Carolinian - we don't, insofar as I'm aware, have the PBA card but it's a common enough thing to see folks with the local equivalent, a sticker, given for donating to the local PBA group on the lower-left hand corner of the rear windshield, such that an officer would see it when walking up to the window.
Now I have no idea of it's efficacy, but I've bumped into a few folks who swear by it. Like the card it would be good for, at best, a warning on a speeding ticket or another basic moving violating. Of course I've gotten the same treatment by simply being respectful to the ticketing officer, so who knows? As gfodor mentioned[0], there are likely certain dynamics to the situation and I can imagine an officer seeing that as too on-the-chin.
[0] - https://news.ycombinator.com/item?id=16208934