Given the vastness of interplanetary distances (a minus) and the billions of years of existence of the universe (a plus) I sometimes have a tendency to believe that the one possible method, of willingly or unwillingly, "broadcasting information" is to seed or "broadcast" life. It is very, very slow but it has billions of years at its disposal, the process does not necessarily needs inteligent life to start or to keep on going and it could have a tree type of expansion, it looks like a very robust carrier method to me (is it?). Now that we have a "carrier" we only need to modulate it in order to send information about ourselves (if we wish to...) Maybe advances civilizations have done that and there is some "modulated" DNA floating around or just unmodulated DNA when it was sent by chance or when its mission was only to colonize.... I think that efforts, if any, to find some encoded message in our own DNA have failed.... so this is just another wild speculation but ...