The decorous behavior of persons in public, in the past, was largely governed by said 10 Commandments. In the past, posting them wasn't necessary because they were inculcated from a very young age in nearly everyone.
I hear a lot of people say that, but I have to wonder if it is entirely accurate, given the nature of the 1st Commandment.
Did 'polite society' really expect non-Christians to hide their faith?