One of the game's fan managed to find the in-game location of the boss. He paid his tribute with the help of a backpack and the piece of paper. The image has gone viral among the game's fans. You can see it here.
Even before this event, the developers of The Division has paid their respects to the victim of the game patch, Bullet King, on Twitter. You can find the post here.
While the story may or may not seem strange to you, what happened is the developers have fixed a popular in-game bug that allowed players to farm the named boss repeatedly. This allowed many players to receive a lot of loot faster than it was planned by game developers.