Like pulling teeth tonight. Anyway...
You're using a slightly customized version of the Journalized Blue theme, which provides a limited range of places we can stick this. Does just above the date on a post sound good? Hope so, because that's where I'm helping you add it.
In Journalized Blue's Main Index (index.php) template (accessed through the Theme Editor, or offline in a text editor), look for this line:
This, obviously, is what outputs the date. So the "you're not on the home page" text doesn't get lost here, we'll duplicate the layout used by the_date() by sticking the text in an
<h2> element instead of a
<p>, as I have it from my last reply. In other more explanatory words, on a new line just above or before the one used by the_date(), insert the following:
<?php if(!is_home() && !empty($_SERVER['HTTP_REFERER']) && !strstr($_SERVER['HTTP_REFERER'], get_bloginfo('home')) ) : ?>
<h2>This is not the homepage of <?php bloginfo('name'); ?>, you are reading one of our posts. Go <a href="<?php bloginfo('home'); ?>">HERE</a> to visit our homepage.</h2>
<?php endif; ?>
Save and have fun.