It was an old custom on Earth that was once popular. Humans would paint stones with pretty pictures, happy sayings, and then, when they had a fairly large collection done, would take all of these intricate stones and scatter them all over the place so other people could find them. Often with a URL on the back for people to log in with a picture of the stone to show it was found and where. A way to brighten a person's day. That person would then be encouraged to take the stone out and set it somewhere so someone else could find it. And let that cheerfulness spread. Some old customs don't seem to die, even as humans have spread through the universe, so have the pretty stones. -- Anon Guest
It was a smooth river stone that was light years from the nearest river. Large and flat and painted with a contrast code that could easily be read by any datareader. The other side of the stone, the one that had been facing up, had a stylised image on it. What it was a stylisation of was something Techie Del was unfamiliar with. Humans had been here.
Just how and why a Human would leave a river rock stuck to the underside of a desk in a derelict vessel was a mystery to Del. Further, that derelict had been marked for complete salvage by a roaming band of scavengers working the very same wreckage Sargasso. Since it had been painted, Del guessed that it was of some cultural significance and put it aside for analysis.
She never expected a rock to be a message in a bottle. After her shift was over, she scanned the code left on one side and found a message and a link to a social site called Dude, Where's My Rock? It was a long-term cross-galactic game. Of course it was. Humans were baffling that way. This game had been going on for longer than an average Human lifespan, so it was a decent bet that the hands that had painted this stone were in their grave by now. There was a message.