how to check whether calvin klein's eternity perfume is fake or original?

I've bought calvin klein's eternity perfume few days back. but i doubt whether it was fake or original. Is there by anyway i can check it? Most of the people around me couldn't smell it but the smell do stick on the shirt (but not that strong). Is there any specific mark on the box or at the bottle itself to make sure it is original?thanx

Probably depends where you bought it from; if it was a reputable dealer or not.