Now this is an interesting bit of unknown history. According to Al Nilsen, who at the time was the Director of Marketing for Sega of America back in the 90’s has revealed an unknown tid bit regarding Sonic 2’s release. That being, the cartridges were to be a little different to the usual cartridges which were out on the market. Sega had planned to make Sonic 2’s cartridge stand out from the crowd.
Sonic 2 had a rather large marketing campaign behind it known as Sonic 2’s day and a scrapped plan was for the initial release of games to have holographic cartridge labels. Mr Nilsen recently showed off the labels via twitter and said that the reason they didn’t go ahead is that it was too costly.
Source: Al Nilsen’s Twitter