Tracking::getSignKey

static function getSignKey()
{
	$key = ConfigOption::get('sender', self::CUSTOM_SIGNER_KEY, null);
	if (!$key)
	{
		$key = ConfigOption::get('main', 'signer_default_key', null);
		if (is_string($key))
		{
			ConfigOption::set('sender', self::CUSTOM_SIGNER_KEY, $key);
		}
	}

	return $key;
}