To commemmorate the Haymarket Massacre in Chicago in 1886, where protestors were campaigning for the 8 hour day (something which they eventually won, and you can all thank them for that). An unknown person chucked a bomb at the police and 7 anarchists were subsequently sentenced and hanged in what was clearly an ideological attack on the labour movement.
Sweet video. Thanks for the mention <3
Happy birthday, LSF!