/**
 * Implementation of hook_form_alter().
 */
function user_form_alter(&$form, $form_id) {
  // Add checkbox for settings to the node type form.
  if ($form_id == 'node_type_form') {
    $type = $form['#node_type']->orig_type;
    $form['workflow']["user_signatures_$type"] = array(
      '#type' => 'checkbox',
      '#title' => t('Show user signatures for content type.'),
      '#default_value' => variable_get("user_signatures_$type", 0),
      '#description' => t("If enabled, users' signatures will be appended to the end of all posts of this type and any of its comments."),
    );
  }
}