Drupal Search API Placeholder && Front Page?
Check for drupal_is_front_page()


  Return value
  
  Boolean value: TRUE if the current page is the front page; FALSE if
  otherwise.


function THEME_form_views_exposed_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if (isset($form['search_api_views_fulltext']) &amp;&amp; drupal_is_front_page()) {
    $form['search_api_views_fulltext']['#attributes']['placeholder'] = t('Search Text here...');
  }
}