I haven’t seen stickers, but Facebook is full of stories like: “I was a Target, and there was this weird guy, and I felt weird, so we went back to our car, and this lady picked him up in A VAN, and once they saw we were in our car they drove off. We called the police and they said that there were gangs of people stealing kids for sex trafficking.”
Or:
“I was at rest stop on the highway when I took my kid to the bathroom, and there were two women in there, and I heard one of them say, ‘The little blond girl.’ We didn’t stop to wash our hands, we just ran back to the car where my husband had parked. Out side waiting were two men waiting out side IN A VAN. We called the police and they said that there were gangs of people stealing kids for sex trafficking.”
I have even seen police departments show screen caps of posts that say, “We have no records of anyone calling us about this. If anything like this happens, you should call us, but also be aware that there is a lot of made up shit on the internet.”
It reminds of the Satanic Panic. My ex-wife is always reminding me to keep my kid near by. 
