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.
If the Lord wants the universe to look natural, how as we as men going to discover otherwise? ID is a fool's errand.
Canard. Those aren't "designed emissions", they're emissions from designed things. Those emissions are incidental to the functions of carpet cleaning and mechanical destruction. "Designed emission" means that the EM signal itself is intelligently designed.
(But in any case, I waive the point as irrelevant. There's no way to cut the Fermilab data such that every top quark is identified, and no background events remain in the sample. In fact, out of millions of top quarks produced, only a handful get reconstructed, but that's more than enough not only to prove they exist, but to measure their properties.)
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.
You said it, right there. The ID proponents are looking for such an effect. But the entire claim of the ID sales force is that such an effect manifestly exists, and they are proposing ID as a candidate explanation! They couch it in terms of "here we have a mystery...oh, look! an explanation!", when in reality it's an age-old supposition in search of some type of evidence that might someday lend it credence. ID has no phenomena, no way to distinguish such phenomena, and gives no reason to expect that such phenomena exist.
Don't keep on insisting that SETI is the same thing, though. It's different on two key counts. First, SETI has unambiguous examples of both designed and natural signals. Both definitely exist in the universe. By contrast, ID--proposed as an explanation of the origin of life--only has one sort of life to ponder, and it's either all designed, or all natural (except for a growing handful of uninstructive exceptions, easily identified by their patents).
Second, SETI has a quantitative, testable method of separating the natural from the designed. ID has only subjectivity: "this looks designed to me" and "I don't see how this could have happened naturally" and finally "OK, it could have happened in one of those several ways, but you can't prove that it actually did, and besides, here's this other thing I don't understand..."
Look at the resistance to such ideas as continental drift and so on.
One of the great success stories of science. When the only evidence was "the continents look like they fit together", it was ignored. When the hard evidence came in, it was embraced. It would have been irresponsible to embrace it any sooner than it was. I say the same thing about ID that I say about free energy schemes: get back to me after you make it work.
That's is only true if the designer's hand is heavy or they seek to be detected.
The entire impetus behind ID is that the designer's hand is so obvious, one must willfully avert his gaze not to see it. But no matter: if the designer truly is a deity (as essentially all ID marketeers believe) AND he wishes his seams not to be visible, we don't have a prayer of ever finding them.
And if the aliens are really tech-savvy and intent on hiding, we won't ever find them, either.