I find it similar to the "Baby on Board" stickers I see on cars.
I really don't care if you've got a baby on board or not - that baby is your responsibility and not mine!
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Absolutely, but there is more to it than that.
I still have one for my six month old son though as, if you are in accident, the emergency services know to look for a baby. (in addition of course to a car seat etc).