At least in spectator mode (if not in-game as well), dropped items should display the name of the player that dropped them, and the name of the owner of the item if this is different.

For example, mousing over a BKB would show:

Black King Bar
Dropped by: Player1

or, if a teammate picks it up and ferries it back to base or realizes he can't use it, it could show:

Black King Bar
Dropped by: Player2
Owned by: Player 1

Information like this would make it easier for spectators to find out who dropped an item on the ground, since they now need to shuffle through everyone's inventory and try to figure out which one is different from when they last saw it. It would also make it easier to keep track of Gems of True Sight and Divine Rapiers (which could also use more information telling spectators which team is eligible to pick it up now).