Not a strawman. In the case of SETI it would be "Natural emissions are broad in frequency and designed emissions are narrow". I'd like to hear of any counterexamples you have. By all means, show that that's silly.
Since you seem to accept the basic idea that searching for the created among the natural is possible, let me toss this back at you. If you wanted to look for some evidence of intelligent design in life, what kind of evidence do you think intelligent design might leave that could be identified? What non-obvious things might you look for?
Now, there's an excellent question. I would look for things that have explicit meaning outside of the context of where the information is found, and little relevance to that context. I'm reminded of the scene in Blade Runner where an electron microscope reveals a serial number on the surface of a cell. A real-world example would be "chimeric" DNA, where jellyfish genes are found transplanted into mice and whatnot.
In any specific case, it might be hard to argue that a pattern of information is definitely not fortuitous. Sometimes, random splotches look so very much like Jesus that otherwise rational human beings bow down and worship tortillas and rusty street signs. Seriously: Google the term Electronic Voice Phenomena and see how easily people fall into such a trap.
If there is a designer behind it, however, the statistical weight of such evidence should pile up quickly. It would be vexing if the hand wrote "MENE MENE TEKEL UPHARSIN" once, and nothing more.
As broadly defined as I defined it, it was a straw man. Narrowed, as you've done, it's not. And you are skipping a step. Designed emissions can also be broad in frequency (e.g., the EM output of a running vacuum cleaner or an atomic bomb). What they are saying is that, "Natural emissions are broad in frequency but some designed emissions are narrow." In other words, if you want to look for designed emissions, you look for the ones that are not easily confused with natural ones. That is, you look for the signals that are characteristically "not natural" based on what we currently know about natural signals and created signals. What ID advocates are essentially looking for is the equivalent -- something biological that's could have been created but can't also be explained by a known natural process.
Now, there's an excellent question. I would look for things that have explicit meaning outside of the context of where the information is found, and little relevance to that context. I'm reminded of the scene in Blade Runner where an electron microscope reveals a serial number on the surface of a cell. A real-world example would be "chimeric" DNA, where jellyfish genes are found transplanted into mice and whatnot.
OK. Now suppose that you've done that and still can't find such low-hanging fruit. What's the next step? Bear in mind that SETI faces the same possibilities. If they don't find any obvious signals or find natural explanations for any signals they do find, do they give up or look for more subtle evidence?
In any specific case, it might be hard to argue that a pattern of information is definitely not fortuitous. Sometimes, random splotches look so very much like Jesus that otherwise rational human beings bow down and worship tortillas and rusty street signs. Seriously: Google the term Electronic Voice Phenomena and see how easily people fall into such a trap.
But that also happens in the other direction. Some people are so skeptical that they don't believe things that were intelligently planned were actually intelligently planned. Look at the resistance to such ideas as continental drift and so on. It's a matter of odds assessment and which way you err. Yes, it's possible to be so gullible that you can be taken in by anything. It's also possible to be so skeptical that you don't believe what's clearly true.
If there is a designer behind it, however, the statistical weight of such evidence should pile up quickly. It would be vexing if the hand wrote "MENE MENE TEKEL UPHARSIN" once, and nothing more.
That's is only true if the designer's hand is heavy or they seek to be detected. For example, the designers of Central Park wanted it to look natural but it isn't. One would have to look at lot more closely at Central Park, perhaps some excavations and such, to find evidence that it's artificial. It's much more obvious that a planned symmetrical flower garden is artifical because it's not meant to look natural. Similarly, it will be much harder to find the human hand in a planted forest that's otherwise untended than in a lawn that's just been mowed. I do think that this raises problems for ID with certain views of God (those where God makes everything happen) but not with others (where God creates and nudges an otherwise natural universe). The ID advocates are not looking for a flower garden planting God. They are looking for the sort of God that would create Central Park.
You are welcome to think that ID is a fools errand, just as people who believe that the odds are against extraterrestrial intelligence, for whatever reason (e.g., religious reasons, applying Occams Razor to the Fermi Paradox, etc.), think SETI is a fool's errand.