I have just done a bunch of server upgrades and some clients are complaining about characters being replaced with a black diamond with a question mark in it.
After researching character encoding I discovered that one of the upgrades had modified my httpd.conf file and added this line.
Commenting this line out returned the situation to normal. I am going to write a quick script to check for non UTF-8 encoding and let these clients know that they are using an encoding method that is becoming non standard.
It was an interesting problem.