What is the true purpose of "baby on board" signs some people stick in their rear windscreens?

I was trying to evaluate whether it might be as an aid to the fire service; i.e. knowing they may also need to rescue a child. But... they don't say how many children, and also, most cars with "baby on board" signs that I see.... don't have a child in them, so maybe could cause a rescue person to waste their time looking for a child that isn't present?

@bloor Pecuniary emulation only, i.e. just a fashion accessory and social signal, which is now passé. There was never any real safety function, bad drivers weren't going to suddenly back off, rescue services gained no useful information from it.