The people at SETI have several useful lessons to teach when it come to detecting non-human design.
1. SETI stands for Search for Extraterrestrial Intelligence. SETI thus searches for non-human intelligence without first rigorously and precisely defining 'intelligence.'
2. In order to detect design, SETI does not first come up with any independent evidence that aliens would or could send us such a signal. Neither must the SETI researchers first see aliens in the act of sending messages before they infer design.
3. While in the process of detecting design, SETI does not consider it important to explain the origin of the designers.
4. What if SETI discovers a persistent, narrow-band whistle in some region of the electromagnetic spectrum? Does this establish the existence of ETI? Where do we go from there? When it comes to the origin of such a signal, why can't we put its origin in the "I don't know" category, as future science may in fact uncover natural explanations for such a signal?
When you consider points 1-4, you'll notice that many common anti-ID arguments are seriously undermined. But there's more.
Of course, SETI works with methodological constraints, assuming a human-like designer in order to make testable predictions. But in what sense is SETI falsifiable? If 25 years of failed experiments do not count as falsification, how many more years are needed? Can we ever falsify the hypothesis that ETI exists? Nevertheless, it is true that SETI is able to test because of its assumptions about a human-like designer. I too have relied on such assumptions when it comes to Intelligent Design, allowing me to better explore the living world from a teleological perspective. I'll have more to say about the remarkable similarities between my ID approach and SETI at a later date.