Death blossom

From The Great Machine

A calling-card for the Narn Assassins Guild, a Death Blossom is a black flower with a green stem that is left on or around those targeted by the organization for assassination. It is considered a warning to the target to bring his or her affairs into order before their 'inevitable' death. It is also employed as a scare tactic, showing the target that someone can get close enough to plant the blossom and, thus, get close enough to kill.