Ouch! This is the part where you say "Just mind your own business".
And if he's concerned about his kids, I think that's his main role as a father to explain to his kids that the sign is inappropriate and take it as a training ground rather than confronting the guy to change his ways.
Most common sticker in my red-neck part of the woods.
Its usually on a 2000 or earlier model of 4WD Ford/Chevy/GM. The driver will be missing a few teeth and the tailgate will typically have a few bullet holes in it.
Saw a funny one when we were in Colorado last month. I should have taken a picture. It said,
"Sugar Daddys Wanted - Inquire Inside". Not sure if it was Lauren Boebert's car or not.