Part V/III. Part I is here.
The earliest reference I cited to the idea of artificial species in stars was from Howard Bond, who said he thought Shklovski & Sagan dealt with it in their book. I finally got my hands on a an early edition.
It looks like Frank Drake and Iosif Shklovskii were first with this idea. From the 1966 edition of Shklovskii & Sagan’s “Intelligent Life in the Universe”:
…we should mention independent suggestions by Drake and Shklovskii that, if not the communication of large amounts of information, at least the communication of the presence of a technical civilization, can be effected through the use of markers. Drake and Shklovskii envision the dumping of a short-lived isotope—one which would not be ordinarily expected in the local stellar spectrum—into the atmosphere of the star. In any case, the material of the marker should be of a type that is difficult to explain, except as a result of intelligent activity.
They conclude with a sentiment I tried to articulate at the end of Part IV.
Remarkably enough, the spectral lines of one short-lived isotope, technetium, have in fact been found in stellar spectra. Its half-life is around 2×105 years. However, technetium lines have not been found in stars of solar spectral type, but rather oly in peculiar stars known as S stars. In fact, as we saw in Chapter 8, the discovery of technetium in the S stars have been used as an argument for contemporary stellar nucleosynthesis. This example illustrates on of the difficulties with such a marker announcement of the presense of a technical civilization. We must know a great deal more than we do about both normal and peculiar stellar spectra before we can reasonably conclude that the presence of an unusual atom in a stellar spectrum is a sign of extraterrestrial intelligence.
I see this as a feature of artifact SETI: anomalies are inherently interesting.