The Arecibo Radio Antenna Sent a coded message to a Globular Cluster, Pioneer 10 and 11 had plaques, and Voyagers 1 and 2 had Golden Records…all using the Universal Language of Mathematics and Science to let some possible extraterrestrial intelligence far in the future understand who we were.
Alexandr Zaitzev is one of the leading proponents of METI (Messaging to Extra-Terrestrial Intelligence).
I’ve had a few chats with him on the Interwebs (or maybe someone who was pretending to be him); he is quite convinced that sending messages of this kind is both safe and a good idea. I am less convinced.