code/Debug/controllers/UtilController.php
public function enableTemplateHintsAction()
    {
        try {
            $this->getService()->setTemplateHints(1);
            $this->getService()->flushCache();
            // no need to notify customer - it's obvious if they were enabled

        } catch (Exception $e) {
            $message = $this->__('Template hints cannot be enabled: %s', $e->getMessage());
            $this->getSession()->addError($message);
        }

        $this->_redirectReferer();
    }
public function enableTemplateHintsAction()
    {
        try {
            $this->getService()->setTemplateHints(1);
            $this->getService()->flushCache();
            // no need to notify customer - it's obvious if they were enabled

        } catch (Exception $e) {
            $message = $this->__('Template hints cannot be enabled: %s', $e->getMessage());
            $this->getSession()->addError($message);
        }

        $this->_redirectReferer();
    }
Enables template Hints