Exactly halfway between Earth and Proxima Centauri, the first starship's scanning maser detected a small artificial object only three million kilometers from its flightpath. In the middle of a complex turnaround maneuver at a third of the speed of light, the AI crew had no time to take good pictures.
  It took another ten years for a specialized probe to fly past the object at even higher speed.

  Mankind's top symbologist studied the scans of the white diamond sculpture. Gleaming austerely, it was a marker of some sort, covered with non-repeating characters and symbols.
From the length of the serial number, there had to be many others like it scattered throughout the universe.
  "By reading this, we've agreed to something," she said.