And if the phrase itself isn't annoying enough, what is the point?
Still, it's not as bad as saying 'Cheeky Monkey on board' or 'Daddy's Princess on board'. I suppose a sign saying 'Child in car' is OK.
But are drivers who are too impatient to care when a human is quite obviously driving the car likely to be more courteous when they it's actually a human WITH A BABY? I guess it tells people to look carefully at the number of passengers in case of an accident. What else is it for?