Documentation

This hook allows the Subscribe2 form output to be dynamically altered to suit the needs of an individual site but applies only to the AJAX popup form.

function my_s2_ajax_form($form) {
    // To remove the 'Your Email:' prompt text from the form
    $form = str_replace('Your email:', '', $form);
    return $form;
}
add_filter('s2_ajax_form', 'my_s2_ajax_form');