News of the discovery of a candidate SETI signal by the Breakthrough Listen Project has been discussed elsewhere on this website. The story is of unusual interest, and likely to persist for some time, so it seemed to rate its own thread.
One aspect of this signal which has not been discussed is the following:

I wondered why the signal, ostensibly from the nearest star to the Sun, Proxima Centauri, was at very nearly just three times the radio frequency of the well-recognized spectral line of deuterium, the doubly-massive form of hydrogen.

Just maybe it's because of the unique structure of the deuterium atom: 1 neutron, 1 proton, and 1 electron. 1 + 1 + 1 = 3. Very simple, of course, but maybe not such a bad way for another form of intelligent life in space to communicate its knowledge about the make up of the deuterium atom.

Then, too, tripling the frequency of the deuterium line also has the advantage of moving the signal into a less noisy part of the radio spectrum, both astrophysically speaking, and with reference to how radio frequencies are used on this planet.

If "they" could choose their frequencies then they would make it exactly 3 times. This I claim is ample evidence of a non sentient origin of this emission.
This could be nothing but a thrust at sensationalism. I have always felt that the breakthrough money might have been better spent. At least they are focusing on this star group since at this "close" distance we might well be able to detect spurious radiation of any kind.

The base frequency could be exactly three times that of the deuterium line. It's already been established that the signal is rising in frequency. A good case can and has been made that this is probably the result of a Doppler shift. This could be caused by either the rotation of a planet, or it's movements around its star.

The frequency would fall, as the source nears the part of its orbit nearest to us, or as the source on a planet approaches a line directly between Earth, and the center of the planet's rotation. Leaving the Doppler shift intact could inform us about the rotation rate of the planet, or its orbital period around its star.

that's right. Good points

Someone has remarked about another potential piece of the puzzle of the Proxima Centauri signal. It could indicate that the signal may really be from intelligent life at that nearby star.

It's simple, really. Proxima Centauri is part of the Alpha Centauri star system. This system has three stars. Two Sun-like stars near each other, and the other, orbiting them distantly, and much less massive, is Proxima.

This system bears a marked resemblance to the unique form of an atom, already mentioned-- The hydrogen isotope, deuterium. The single proton and neutron, close together in the nucleus, resemble the large, Sun-like stars. Diminutive Proxima orbiting them stands in for the sole, low-mass electron.

Is it a mere coincidence that a signal, which has just three times the radio frequency of the deuterium radio spectral line has as its apparent source a system with three stars, and that these three stars are arranged like a deuterium atom? An interesting coincidence, if that's what it really is . . .