Probably an indication that text from a previous e-mail has been included. For instance, one of the settings for OE allows you to append the message to which you are replying or that you are forwarding. I seem to recall that you can set the place where your reply is added to either the top or the foot of the previous message. That would allow for the non-chevron text (i.e. text added by the person sending it to you) to be either at the top or the bottom of the mexssage.
Clear as mud eh?
Hope that helps
ST