#12: protected_title_format

protected_title_format.php

<?php
/**
 * 'Members Only' title for protected posts
 * 
 * @see get_the_title()
 * 
 * @param string $protected Text prefixed to the title for password-protected posts.
 *
 * @return string The filtered prefix text.
 */
function wpdocs_members_only_label( $protected ) {
	// The %s specifier is replaced with
	// the post title after the filter is evaluated.
	return __( 'Members Only: %s', 'yourtextdomain' );
}
add_filter( 'protected_title_format', 'wpdocs_members_only_label' );

http://fotd.werdswords.com/protected_title_format/