SETI greeting, ca. 1970s.
SETI greeting, 1996.
The SETI greeting was a communications protocol developed by 20th century Earth astronomers for the purpose of signaling an extraterrestrial intelligence.
The SETI greeting was intended to be intelligible by any technological sophisticated civilization and conveyed information about Earth's position in the galaxy, information about life on earth, and greetings from Earth languages.
The Earth probe Pioneer 10 was given a plaque on its outer hull that contained the SETI greeting. (Star Trek V: The Final Frontier)
Earth astronomer Rain Robinson transmitted a SETI greeting to the USS Voyager in 1996. (VOY: "Future's End, Part I")