A publicity card commissioned by the French laboratory Le Brun for Megably, with art by the famous French cartoonist Jean-Jacques Sempé, known only as Sempé. 

c.1961

This one says:
... N'interrompez pas constamment les conversations particulières pour donner votre avis... 

The conversation bubble says: 
A mon avis…

English translation:
... Do not constantly interrupt specific conversations to give your opinion... 

The conversation bubble, in english, says: 
In my opinion…

Dimensions:
7.2 in wide
10.3 in