NGC® Certification is a special kind of authentication performed by the Numismatic Guaranty Corporation, widely considered to be the most reliable service in the world.
All NGC® coins are permanently encased in tamper-proof plastic holders, as seen above. This is done to make it impossible to switch out the original coin for a forgery.
You can also use the serial number and grade on the front of the case to look up the coin on the NGC® website, which will show photos of that very coin at the time of its authentication. This way, even if coins changes hands, it is always easy to verify that an item is completely authentic.
For more information and to verify a coin's authenticity, visit: www.NGCcoin.com/verify