A sign isn't going to slow down idiot drivers or make them do anything that they weren't already going to do. (However, maybe a shotgun barrel....?)

OTOH, if there's an accident, all the baby paraphernalia will scream that there should be an infant nearby. Years ago, there was a rollover, the unsecured baby was flipped out of the rolling car. As soon as the first officer hit the scene, he knew there was a baby nearby-- and it was, 'way over in the weeds, totally unconcerned.

Sue