Example given by mototribe

How to show countryicons with the user info - 7.x:

Use http://drupal.org/project/countries module and add a country field to the user entity.

A. Using a view:
Create a view to show users, add the user country field to the view and select fomatter "country icon image shiny". This will show the country flag.

B. Modifying the theme:
To show user flags with comments modify template.php of your theme (Bartik in this example):

function bartik_preprocess_comment(&$variables) {
  $comment = $variables['comment'];
  // Full load user
  $user = user_load($comment->uid);
  // Now access your field
  $country = field_get_items('user', $user, 'field_country');
  // krumo($country);
  if ($country) {
    $variables['user_country_name'] = $country[0]['safe'];
    $variables['user_country_flag'] = theme('countryicons_icon', array('code' =>  $country[0]['iso2'], 'iconset' =>  'shiny'));    
  }
  else {
    $variables['user_country_name'] = '';
     $variables['user_country_flag'] = '';
  }
 }

add the 2 variables to your comment.tpl.php

<?php print $user_country_flag; ?>
<p class="comment-time">
   <?php print $user_country_name; ?>
</p>