How to add a selector to wp_loginout

http://codex.wordpress.org/Function_Reference/wp_loginout

there is probably no parameter to add an selector.

however, wp_loginout() has a filter hook 'loginout' which you could use to influence the output – i.e. to include a selector.

for instance by adding a filter function like this to functions.php of your theme:

add_filter('loginout', 'loginout_selector');
function loginout_selector($text) {
$selector = 'class="woo-sc-button"';
$text = str_replace('<a ', '<a '.$selector, $text);
return $text;
}