It works fine on 3.8.2? I just tested it.
Make sure you are adding it as a plugin and not a product. You may see a link saying no link. To change that go to ACP > Plugins and Products > Plugin Manager and edit "Hide Links from guests"
In the plugin PHP code box find
return '<a href="register.php" title="Please register first or login" target="_blank">No Link?</a>';
And do any of the following.
To show a link that goes to registration page
Replace that code with return '<a href="register.php" title="Please register first or login" target="_blank">PLACE TEXT HERE</a>'; And replace the "PLACE TEXT HERE" with what you want the link to say.
For no link to appear just text:
Replace the code above with this return 'PLACE TEXT HERE'; Replacing "PLACE TEXT HERE" with what you want the error message to say.
Note that you may think this is not working because there is no styling around it and it looks like a post but I can assure you it works on 3.8.2