I think all those signs of radio and other frequencies made us vunerable and easy to find for any civilization, with good or bad intentions...
If suddenly appears unknow spaceships on Earth, i guess in a brute statistic 1 in 10 people should know ID that is not from Earth. That mean around 70 milions earthlings could identify if this is from Earth, or even this not from Earth, by some similarities with our tech, design and languages.
So, first we need teach everyone things about space, time, size, volume, mass, gravity, physics (even without calculations for those who doesnt like of mathematics...) in a way that if something of outer-space come here and try to conquer, or kill, or kidnap, or even make friendship, everyone on Earth should ID that's not from Earth.
Teach, education, and knowledge, is the best way to evolve a civiliization...
and if they reach us in short-time space-trips by hacking the space-time and they want to destroy us... Man, surrender.... cause there's no atomic bomb capable to destroy them in this universe, cause they tecnology is just so fucking evolved to do those things that we are just primitives for them, even with our tech...