Never send something that you would mind seeing on the evening news. Be careful when using sarcasm and humor. Without face to face communications your joke may be viewed as criticism. When being humorous, use emoticons to express humor. These frequently send a string of control characters that wreak havoc on some types of terminals.
Flames are, unfortunately, common.
Keep your signature file under six lines long. These pages may not be copied or reproduced in any way without written consent of the author.