There is one way. You are required, though, to send a message. If you are using older version, upon sending a message, skype will notify you that your message can not be sent. But if you are using v.4 and above, you will see the spiraling icon which means your message is not sent to the recipient. These two examples mean that the user your are trying to contact is really offline.
If, however, by chance you did not receive any kind of sending failure notification upon sending a message, then the recipient has invisible status.
>;)
