Assassin's spear

An assassin's spear was a magical shortspear that, when thrown, granted the thrower invisibility. An assassin's spear was worth around 8000 gold pieces.

Realmslore
The spear was made by a master assassin in the city of Amn who had become bored with all the methods of killing people he had tried. He wanted to be able to kill people in a large crowd in a spectacular fashion and yet still escape undetected. He created five weapons in the form of spears, since these were often carried by city guards, but told no one of their powers. These five items were later scattered across Faerûn.