bid/module/Listings/view/listings/cart/checkout.phtml

<?php
/**
 * @version 7.9 [rev.7.9.01]
 */
if (empty($this->loggedInUser['id'])) { ?>
    <blockquote class="bq bq-info">
        <a class="dialog-box"
           href="<?php echo $this->url(array('module' => 'members', 'controller' => 'user', 'action' => 'login-modal')); ?>"
           title="<?php echo $this->_('Log In'); ?>">
            <?php echo $this->_('Already Registered? Click here to login.'); ?>
        </a>
    </blockquote>
<?php } ?>

<?php echo $this->form; ?>