How to add asc and desc sort symbols in drupal views?
Implement theme_tablesort_indicator(). Please replace your theme name with example

function example_tablesort_indicator($variables) {
  $style = $variables['style'];
  $theme_path = drupal_get_path('theme', 'example');
  if ($style == 'asc') {
    return theme('image', array('path' =&gt; $theme_path . '/images/arrow-asc.png', 'alt' =&gt; t('sort ascending'), 'width' =&gt; 13, 'height' =&gt; 13, 'title' =&gt; t('sort ascending')));
  }
  else {
    return theme('image', array('path' =&gt; $theme_path . '/images/arrow-desc.png', 'alt' =&gt; t('sort descending'), 'width' =&gt; 13, 'height' =&gt; 13, 'title' =&gt; t('sort descending')));
  }
}