Great module - but the template code produces some spurious closing UL tags that make the Joomla page fail XHTML validation (at http://validator.w3.org).
So to fix it (until the developer fixes it), after module installation open the following file in a text editor:
/modules/mod_signallogin/tmpl/default.php
... and find and remove the two closing UL tags (), resaving the file afterwards. This should allow your page to now validate (if that's important to you!).