You could put this in the module template which is in the file tmpl/default.php
For example to put it just before the date and author edit line 18 from
<span class="dateAuthor"><?php echo $item->author; ?>
to
<span class="dateAuthor"><img src="hot-icon.gif" /><?php echo $item->author; ?>
obviously change 'hot-icon.gif' to your image URL.
Or you can put it in the read more text parameter, that can accept html so just put the <img> tag as part of the read more text, eg
<img src="hot-icon.gif" /> Read More..