C'est jaune, c'est moche...

My French teacher told me that French people never admit that they work out at the gym.  Instead, they will claim to be "naturally this thin."  It's socially unacceptable for French girls to go to the bathroom.  They tell others that they're only going "to powder their nose."  The French have a reputation of being slightly more self-conscious than the rest of us.  Image is everything.
Recently, France passed new road safety laws requiring everyone to keep bright yellow life vests in their cars at all times.  Yet, presentation is so important in France that many people would rather break the law than wear a neon-colored jacket.
Thus, considering French culture, the government needed the help of Karl Lagerfeld to enforce this law.  Karl Lagerfeld is known to practically everyone in France, even males, and he reigns as its most important fashion icon.  As the designer of Chanel for many years, he sets the trends in France, and people listen to him.
Only in France will you see this kind of ad.  Lagerfeld is dressed in his standard suit, gloves, and sunglasses, but instead of at a fancy party or a fashion show, he looks out of place standing in the middle of random road.  The location is somewhat far from an urban city, where people are used to seeing him.  Most noticeable is the bright yellow vest he is wearing over his fashionable clothes. 

The statement in the ad, when translated, reads "It's yellow, it's ugly, it goes with nothing, but it can save your life."  The ad tries to communicate to the audience an ethos appeal.  It argues that even Karl Lagerfeld, the leader of fashion, is willing to sacrifice his image in order to stay safe; therefore, there is no shame in wearing this unfashionable vest.