Let me clear up a common misconception. When most people say writing in code, what they really mean is writing using a cipher. A code is when a symbol, word, or phrase is used to stand for a different word, phrase, or sentence. A cipher is were each letter in a word is represented with a different letter or symbol.
The dash is a punctuation mark that is similar to a hyphen or minus sign, but differs from both of these symbols primarily in length and function.
The dash is often combined with ordinary quotation marks. For example, in French, a guillemet may be used to initiate running speech, with each change in speaker indicated by a dash, and a closing guillemet to mark the end of the quotation.