Introducing the Mortal Cup, the instrument in which Shadowhunters can be made.
@mortalmovie posted this photo with a clue: I have a very strong band of friends. Everyone seems to think it's Valentine, but know one knows for sure. Does Valentine have friends, or is he revered by people with an undertone of fear? My guess is we'll see Valentine another time, but you be the judge.
Also you can see the first clue photo here too.