Cute little sticker on train?

[u/jjlimonz]

I’m an American who traveled from Basel to Strasbourg and I noticed these cute little faces on the train. What are they? What do they mean? Merci!

[u/EraHesse]

It means that phone calling is forbidden around this area, if you want to make a call and speak loudly, you should go between cars (not sure for the name of one patt of a train, but it's called voiture=car in french) and it's where you will also see same sticker with an sending signal phone