Detecting design or intent in nature

[Heywood]

Intelligence is not human. Intelligence is intelligence.

all your observations of it -are-. Your conclusion will have to concede, if you're still pretending to base it on observations, that it was human intelligence that created these systems, even the system that yielded human intelligence

...because that's the only intelligence you have observations of to make statements from.

You're making the same blunder that Esquilax is making. You are conflating intellect with human. They are different qualities. They are not inextricably linked. Consider this proposition:

Only human intellects have been observed transmitting the value of pi via radio waves.

It is really two propositions:
1. Only humans have been observed transmitting the value of pi via radio waves.
2. Only intellects have been observed transmitting the value of pi via radio waves.

Now suppose we observe the value of pi transmitted via radio waves originating from a source from which no human could be or have ever been. Such an observation would falsify proposition 1 but it would in no way falsify proposition 2. The two propositions are not inextricably linked.

Observing an intelligent signal would from another solar system would be an indirect observation of non human intellect. Observing an evolutionary system which could not have required humans falsifies the proposition that all evolutionary systems require humans. It does not falsify the proposition that all evolutionary systems require intellects. As long as all evolutionary systems whose circumstances of origins are known.....are found to require intellects.....the proposition that all evolutionary systems require intellects is still very reasonable. It is much more reasonable than the contrary proposition held by many atheists which has virtually no observational evidence to back it up.