See RulesForUsingHyphensAndDashes.
Although there was discussion on EmDashInAscii, it primarily focused on our signature convention. If the use of "--" as a dash breaks the signature macro, the signature macro is already broken. Shall we next start changing all of the decimal separators here, so that 1,234.56 becomes 1.234,56? It is both wrong and offensive to traverse page after page imposing this change -- so much so that I think it constitutes vandalism. Please stop.
-- TomStambaugh