How do you identify fake Tiffany?

At a party the other night me and my friends found a necklace and they all were like oh thats fake Tiffany. I had no clue how thwy could tell like that I dont have any fake or real so I can not compare. Also I dont care much about Tiffany but I kind of want to know now.|||you look at the clasp , but if you found this necklace at a party you must return it to the person whom is lost it , ask them to describe it before returning it this way you know that it goes back to the rightful owner.