SETI greeting, ca. 1970s.
SETI greeting, 1996.
SETI, or "Search for Extra Terrestrial Intelligence", was a 20th century Earth effort to detect, and contact alien intelligence.
The SETI greeting was displayed on a plaque on the hull of such NASA probes as Voyager VI and Pioneer 10. (Star Trek: The Motion Picture, Star Trek V: The Final Frontier)
In a revised 1996 Earth timeline, a young researcher, Rain Robinson, detected the USS Voyager and transmitted the standard SETI greeting. (VOY: "Future's End")