Link to send private message to current user in the node (author of the content)?
I did it with a Display suite custom code field. With it I am able to use some PHP code.

global $user;
// If the user is anonymous (role=1) show this; otherwise show nothing.
if (isset($user-&gt;roles[1])) {
  print l(t('Contact member'), 'user/login', array('attributes' =&gt; array('class' =&gt; array('radius', 'button'))));
}


So, when the user is logged-in, this code above will be replaced with the contact member link (Send author a message).