The Black Hand was the secret Serbian Nationalist organization. Some historians say it was more a mythical concept than a real organization, and others, especially fiction writers, treat it like a cross between the Cosa Nostra and the Illuminati.
It was another name for the Mafia in Godfather 2
I was out at the Trap range shooting one of my older guns, a Browning Auto 5 that was one of the last one’s made in 1914 before the Belgians had unwanted guests. A guy asked me about it so I gave him the spiel. He had an accent I didn’t recognize. Turns out he was from Serbia. His last comment was “Browning good gun, Gavrilo had one!”
That was weird.