The number of the original BD is 15018, of the remastered release
21520.
If the plastic wrapping is still present, the anti-theft tags say: "Fifth Element, The RMSTD BD".
The colour on the artwork of the remastered version is more "metallic", on the original lighter as well as redder.
On the backside, down, the new remastered version will have an ABC logo (triangle) and Dolby TrueHD as well as a "FULL HD 1080" logo. The circular PG-icon is in the middle. The original doesn't have the three logos I mentioned (it has a single "A", down left, for region-A) and the PG-circle is on the left quarter.
Down in the middle (where the new version has its PG-circle), the old one has "15018LIT" printed, more to the right "Printed in U.S.A.". The new one has "Printed in U.S.A." at the same place as the old one, but immediately above it: "21520LIT".
Remember just one of these differences when you go shopping and they will not be able to fool you!
Cees