Our civilization produces electromagnetic racket. It is comprised of every intentional broadcast: television, radio, satellite, and so on. There are also unintentional electromagnetic noise sources such as electric motors, power generators, light bulbs, the computer you're using to read this, and so on.
All this electronic racket is racing away from earth at the speed of light, which is how fast electrons move in a vacuum. This process began when humans first began building machines that create electromagnetic fields, back in the mid-to-late 19th century, but it really ramped up after the development of commercial radio broadcasting, which became ubiquitous in the 1920s. Since it is now 2002, the front of this electromagnetic racket can be thought of as a sphere about 80 light-years in radius, with earth as its approximate center. (This naturally discounts solar and galactic motion vectors.)
Every bit of this electromagnetic racket is information that, in principle, can be interpreted by an external party with the appropriate equipment. Decoding our radio and television transmissions should be easy; they were designed to be easy to decode. Encrypted traffic will be a little harder, but possibly quite easy for the external party. From these intentional transmissions, they can learn about Britney Spears, political scandals, diet fads, and infomercials. From the unintentional transmissions (which should be easy to distinguish), they can learn of the state of our technology.
I'd argue that any third party (external of humanity) that is capable of detecting and gaining information from our electromagnetic racket must be much more advanced than humanity is currently. They would need something much better than our radio telescopes. That makes me think that they would see us existing in a earlier developmental phase than they. They could see our weaknesses and our stupidity for what it is: our electronic childhood. This is the stupidity front. Perhaps they will understand it, because they went through a similar phase themselves.
The thing is, intelligent alien life (the 'third party') has been really hard to find. If it's out there, it's probably not close by. It may be thousands of light-years away from earth. That means we will have a long time to advance before the third party will hear our earliest feeble transmissions of Hitler and Stalin, of Vietnam and Auschwitz. If we still exist then, humanity will be beyond these things as far as we are currently beyond the Stone Age. Perhaps our progeny will have met the third party. And then, much to our children's embarrassment... just imagine what happens next:
After being dead for eons, we are vibrantly alive again, in our wretched indignity! And the worst part is, the neighboring third-party gets more and more of this indignity as time goes by. Every Jerry Springer episode. Every WWF match. All of our hardcore porn. Monster truck shows. NPR and PBS, holding the torch of highbrow culture, will represent a tiny fraction of this, as would other things like scientific telemetry. Nonetheless, it would largely be like watching monkeys masturbating in a cage, flinging their own feces at each other.
I'm entertained by this thought. Our lasting mark, our most enduring legacy, dare I say our most profound mark on the cosmos, may be our vast, 160 light-years in diameter, stupidity front. It's our cosmic joke on our distant descendants, who will probably live much better and longer than we do now. Maybe they will make some kind of attempt to jam the transmissions so that no one will know, but I doubt that. I think humanity will be able to laugh at itself by then. Might as well sit back and watch the ancients debase themselves. It will be a good lesson too. We will teach them humility.
And there is consolation for the humanity of the distant future: they probably get to experience the childhood embarrassments of their third-party neighbors too. That should be good for a laugh of its own.