To put your mind at rest you could register your product for warranty with Cowon, or just mail them the serial number on the back and ask for confirmation.
Like others I'd be amazed to see a fake of such a niche product. Fakes tend just to be superficial imitations: imagine the r&d to mimic the BBE sound enhancements and complex eq of a Cowon!
There is one way uncannily accurate 'fakes' reach market: when a Chinese subcontractor for a major brand does a clandestine production run to sell through back channels without knowledge of the brand. Again I can't see it in this case: you could maybe hide a few extra Ford cars in a production run but unexplained extra Maseratis would soon be spotted by the owner community or the manufacturer. And the Cowon is certainly more of a Maserati than a Ford (as you will find if you go looking for spares or accessories!)