Tracking::getSign

static function getSign($value)
{
	static $cached = array();
	foreach ($cached as $cache)
	{
		if ($cache[0] == $value)
		{
			return $cache[1];
		}
	}

	$signer = new Signer;
	$sign = $signer->getSignature($value, static::SIGN_SALT_ACTION);

	$cached[] = array($value, $sign);
	if (count($cached) > 10)
	{
		array_shift($cached);
	}

	return $sign;
}