I've never 'got'

My theory is that at least some of these drivers are up to no good, don't have a kid, but have that in the window so they're less likely to get stopped.

I never knew what they were for until someone told me recently that it was to alert the emergency services if they’re faced with checking multiple cars in the event of a pile up.

I think they’re obnoxious and the emergency services should be allowed to get on with their job however they see fit.