Re: Here is another possibility
In the absence of planetary ephemerides for distant extrasolar planets, how could we transmit a message reliably?
The answer may be by transmitting a sliver beam. The beam would not have a circular cross-section, rather it would be rectangular - very thin and extremely wide. The beam would cover between 0.5 and 2 AU distance from the star. As the planet orbits it will cross this line once per year and be able to receive. The transmission would appear to be an annual blip.
Such a SETI signal might be detected by its annual periodicity.