Usually original copies, at the back of the dvd/cd in the center, usually they have IFPI ####(numbers), that's if you already bought it though.

Just make sure you've seen the original cover before, lol, I've seen a pirated version of New Police Story, the front cover is almost exactly like the original box cover, difference is Dave Won'g's picture is cropped onto the cover.

I also noticed some pirated stuff have a sticker on it of some sort. But that's just chinatown in sydney. Lol, the store I go to in Dixon Street, chinatown, have legit and pirated stuff hand to hand.