尝试以下操作（不要忘记替换图标URL）：

add_filter( \'display_post_states\', \'password_protected_icon\' );

function password_protected_icon( $post_states ) {

    $text = __(\'Password protected\');
    $pos = array_search( $text, $post_states);
    if( false !== $pos )
        $post_states[$pos] = \'<img src="http://i.stack.imgur.com/aIDa6.png" title="\'.htmlspecialchars($text).\'"/>\';

    return $post_states;
}