a stupid freaking yellow sign that most commonly mothers put on their car window to signify the fact that a baby is "in the car" Which basically means drive carefully which you should be doing anyway and who cares? Good on you for having a baby, you dont have to share it with the world because surprisingly no one else cares.
Franz: "Oh look, those people have a baby on board, i can tell by that yellow sign that hangs in their window."
Citronella: "How stupid, what are we meant to do? Drive slower? Donate some money? Beep our horn? What are they trying to prove. Friggen idiots."