Site slogan not displaying?

For some reason I am unable to get the site slogan to display.

I'm using this code:

<?php if (!empty($site_slogan)): ?>
  <div id="site-slogan"><?php print $site_slogan; ?></div>
<?php endif; ?>

I have entered the slogan on the admin/settings/site-information page and a search of the database shows it has be stored.

Site slogan appears to be determined as being empty.

This test confirmed this:

<?php if (empty($site_slogan)): ?>
 <p>SLOGAN EMPTY</p>
<?php endif; ?>

As 'SLOGAN EMPTY' is rendered in the HTML output.

Anyone know what is going on here?