What does a diamond with a question mark represent?

A diamond (or square) with a question mark in the middle is not an emoticon, but a "replacement character." It is displayed whenever a character is not recognized in a document or webpage.

Replacement Character - Diamond with Question Mark

Most often, a character is not recognized because the character encoding is incorrect or is not supported. Text documents and webpages often define a specific character set, or "charset," which determines how characters are interpreted. For instance, a webpage may define the charset to be "ISO-8859-1." If the text contains characters that are unique to the "UTF-8" character set, they will not be displayed. Additionally, even if a special character like the copyright symbol (©) belongs to the ISO-8859-1 character set, it may not be displayed correctly since the character encoding is incorrect.

Instead of displaying an unknown character as a blank space, word processors and web browsers may display it as a replacement character, or a diamond with a question mark in the middle (�).

Since different character sets use the same codes for standard letters and numbers, most characters will still be displayed correctly even if the wrong character set is defined for a document. Special characters, such as symbols, uncommon punctuation marks, and asian characters are the most likely to be replaced with replacement characters.

NOTE: While the diamond with a question mark is not an emoticon, it is still possible to use the replacement character as part of an emoticon (e.g., ^�^ might be a bird). However, it is best not to use the replacement character in emoticons since people may think it is supposed to represent a different symbol.