No don't use conditionals, the easiest way is to do this.
Edit the .xml, scroll to find (around line 206):
Code:
$templater = vB_Template::create('post_thanks_box');
$templater->register('post', $post);
$templater->register('post_thanks_box', $post_thanks_box);
$template_hook['postbit_end'] .= $templater->render();
}
Change this line:
Code:
$template_hook['postbit_end'] .= $templater->render();
To this:
Code:
$show['post_thanks_box'] = $templater->render();
Then in your
postbit_legacy or
postit template find:
Code:
{vb:raw template_hook.postbit_signature_end}
And after that add this:
Code:
{vb:raw show.post_thanks_box}
Now it will show inside the post, below the signature, even if the user has no signature.