Custom prefix for each value of a multi-value field
You can use form_alter function to do it:

/**
 * Implements hook_form_alter().
 */
function your_module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id == 'article_node_form') {
    $form['field_number'][LANGUAGE_NONE][0]['value']['#prefix'] = '$';
    $form['field_number'][LANGUAGE_NONE][1]['value']['#prefix'] = '€';
  }
}