Except SETI is looking for a known type of signal that is only generated by artificial means. (Does not require the "God in the gaps" idea).
Exactly how does one "detect design" using information theory? There are a lot of things you can do with Kolmogorov complexity (e.g. finite state machinery detection), but "design" isn't an information theoretic term. In fact, all the plausible answers for what you mean by "detect design" have consequences that you probably won't like; it necessarily implies limits and restrictions on the designer's capabilities (i.e. the designer can't be the Christian God).
When you explain how all this works, go ahead and use all the big words you like; I work on the bleeding edges of information theory in the real world and am thoroughly familiar with the mathematics and implications.
Designs are clearly present in nature. A Designer is not. The apparent design results from natural selection. This is a process whereby trillions of experimental combinations of genetic material are constantly being tested. What works survives and reproduces. The failures die off. Dembski is not a biologist and does not understand that the instruction sets (i.e., the genomes) for the "designs" he purports to model are hodge-podges. All the accumulated change of every species' evolutionary history is written into the genome. The genomes are not fixed -- mutations occur at known rates -- and every "design" has precedents or is shared among species. The simplest refutation of Dembski's ID theory comes from the manner in which unrelated bacteria share genetic material through plasmid transfer or by viral transduction. In other words, known biological processes preclude the possibility that any individual life form on this planet was ever purposely designed.