All of the SETI projects we've seen so far
are passive SETI, designed to listen
(look for) signals. But another possibility is
to actively broadcast signals that we want
extraterrestrial civilizations to receive and
understand.
This is in addition to all the KNAU radio
station and "I Love Lucy" broadcasts that
we are constantly sending into space.
In 1974, this image was transmitted toward
a globular star cluster that is around
21,000 light years (7000 parsecs) away.
This message was transmitted as a series of 1s and 0s:
0 0 0 0 0 1 1 0 1 etc etc.