The Watchers Council seeded star systems with beacons containing information useful to civilizations at the cusp of leaping into the stars. These beacons were called Karvassian Buoys, and they created as much trouble as they prevented.
The Watcher's Council dictated a strong non-interference doctrine, insuring that primitive civilizations would not be unduly influenced or interfered with by starfaring civilizations. However, after watching thousands of promising civilizations blow themselves up on the cusp of achieving interstellar flight, the Watcher's Council decided to interfere in one, specific way:
They would give advice to civilizations on the cusp of interstellar flight.
This was not simply due to kindness. After dozens of self-destructions, many aggressive phantom delegates were left without anyone to delegate for. Phantom delegates fought for measures to insure their life's work would not be wasted by the sudden self-destruction of their wards.
But interference is a difficult topic, especially given the rise of the strict non-interference policies that govern modern xenosociology.
After decades of bitter argument, the Karvassian Buoys were created. Containing only knowledge to prevent the most common types of self-destruction, they were seeded around thousands of stars.
The buoys are solid-state beacons intended to last for millions of years. They use solar radiation to create faint but detectable radio signals, and are placed such that a civilization exploring their own outer solar system will almost certainly notice them.
Since the buoys are not allowed to teach math or language, they contain thousands of dioramas. When light moves across them, the dioramas reflect it in different patterns, creating a visual that can be interpreted as a cautionary tale.
The difficulty was not in physically creating the dioramas, but in making them actually explain things.
In the end, the Karvassian Buoys are arguably the least understood communications ever transmitted. There have been many communications that had unintentional side effects, such as those seen in The Stolen Years and the Happy Hat Incident and even the N-dimensional Kandar Lithoglyph... but the Karvassian Buoys are a fascinating example of how to get things wrong, with every step recorded in detail, from start to finish.
Dozens of civilizations found their buoys and achieved a relatively normal superluminal status. Most of them even joined the Watchers Council, replacing their phantom representatives.
However, only three of them actually understood the buoy's messages.
The others universally misinterpreted the buoy's nature.
Statistically, there were more subluminal civilizations taking it as a warning that some kind of extra-galactic enemy returned every galactic cycle to eat all life.
However, knowledge that there were nonaggressive spacefaring species was often enough to get them past the dangerous phase, regardless of message. Because of the buoys, they readied to meet potential friends instead of potential conquerors.
Arguments continue over whether the buoys actually helped. In hundreds of cases, discoveries of the buoys ended up twisting the civilizations beyond repair.
While most failures lie outside the Bottlenose Nebula, the most impressive catastrophic misunderstanding was the three-way self-destruction of the Kylque Kin.
This has largely led to the noninterference doctrine being strengthened. No further buoys are being deployed.