The condition says to not allow certain coding characters that are considered unsafe in a Referer string, but I think allowing the angle brackets < > in a Referer string is not that big a deal. Allowing the angle brackets in a Query string security filter would be a big deal. ;)
Actually it was just the website preview that was not being grabbed. The images were are retrieved successfully with or without the security rule modification. Personally I actually like that fact, but for the type of site you have you would probably want both your site and image files to be grabbed.