replacement character

The replacement character you see often � is the question mark inside a diamond.

It is used to indicate problems when a system is unable to render data to a correct symbol. Often experienced when cutting-and-pasting from Word into HTML, it's recommended to use plain text otherwise you may experience a variety of gremlins. This is a symbol in the Unicode standard at code point U+FFFD in the Specials table.

NetLingo Classification: Technical Terms