[Lynne]

Turn off post caching on the whole site? Or write a plugin that looks for a string that starts with:
<img src="images/misc/quote_icon.png" alt="Quote" />
and ends with:
<img class="inlineimg" src="images/buttons/viewpost-right.png" alt="View Post" /></a>

And remove it for unregistered users? That is the code from the postparsed table, if the post isn't cached then it is different. Also, that is from my site, your paths may be different - just look in your database to see what they look like.