They advertise the name, the sport, often the jersey number, and they give a good idea of how old a child is. And they are everywhere.
Mother Vickie Intlehouse sports two team decals on her SUV.
"When the kids are in activities or playing sports, they get them and they're proud of what they do," she says.
So on go the decals. And police say that's information a sexual predator could use.
Officer Don Martin of the Tyler Police Department: "They'll use that against the child. They're going to call that name, and again, they're not a stranger as much because they're calling them by name."
"I would rather [strangers] not know so much about us, but when [children] come home and want it put on the car, that's what I do."
The younger the child, the more vulnerable they can be to sexual predators. That's why police say supporting high school sports, are not as dangerous as those advertising younger activities.
"Children that are still vulnerable to predators -- that trust people -- that's the ones we want to be careful for," Martin says.
If a person know the child's name, are they still a stranger? Vickie says she teaches her children to never go with anyone who's not family or a friend, no matter how much they know.
"I teach them that strangers look like every other person. There's no way to tell who a predator is," she says.
And she's also thinking using the child's last name on the decals may be the way to go.