Not sure this is the right category, but here’s a thought experiment:
An anomalous object appears in outer space approaching earth. Inevitable arguments begin as to its origin. Does is have a natural source or an artificial source? Is it a naturally occurring object or an alien spaceship or something else? How could we tell? Are there criteria for artificiality?
This is not a scientific “category” but are we ready to dismiss the question as “outside the realm of science”? I don’t believe that such criteria exist but I strongly suspect that if such an unlikely event were occur, speculations would abound with confidence. Semiotics would be appealed to. “I think it’s a spaceship because it looks like a space ship.” “Symbols (or things that look like symbols) confirm that this is artificial.”
But there is no strict scientific criteria for “artificial” (that I know of).
What’s the point of all this?
If there are established criteria for “artificiality” is it possible to evaluate whether the universe itself bears the criteria?