The above sign can be found on the door of Pope Francis' private apartment at Saint Martha's Guest House at the Vatican. From Italian to English, the sign reads:
IT IS FORBIDDEN TO COMPLAIN.
I don't believe the sign is an infallible pronouncement of the Pope on faith and morals. It is simply his sense of humor (lol). Francis is challenging those who complain to stop and count their blessings. ("Can I hear an Amen!")