Views exposed filter. Добавляем placeholder.

function module_name_form_alter(&$form, $form_state, $form_id) {
  if ($form_state['view']->name == 'view_name') {
    if (isset($form['field_name'])) {
      $form['field_name']['#attributes'] = array('placeholder' => array(t('Placeholder text')));
    }
  }
}