Really? So if you don't have the sign, the fire fighter or ambulance officer won't bother to check all the vehicle for occupants?
Come on.
The arrogant excuse has been that other road users should drive carefully by a car with the sign because there is "precious cargo" on board.
No, the reason other drivers should drive carefully by cars with the sign is because of the parent behind the steering wheel. He/she has had broken sleep for at least 10 months, has been awake since 4am, and is surviving on coffee and leftover baby food for breakfast.
Or maybe the sign is to warn other vehicles that the driver is distracted with a screaming baby in the carseat behind him/her that has just thrown up.
Seriously though, as a mum who spent many years transporting my two kids I reckon that instead of thinking a sign will protect your children from other drivers, you should concentrate on your abilities as a driver.
Don't tailgate, do look ahead (not just over your bonnet) so you can monitor traffic, and check your rear view mirror frequently.
And make sure your child is in the car seat that fits her/him - and consider keeping him/her in a booster seat beyond age 7.