Can anyone tell me?

I don't know if for some reason I'm tuned into to random things right now or if there really are more around, but I have noticed a lot of license plates lately that have the "Amateur Radio" thing on them with the license number being this person's "call sign".
Can anyone tell me what this is all about? I've heard of something called "ham radio" (assuming the ham stands for something and doesn't really mean "pig radio"). In my head, ham radio operators work out of their basements that all kind of look like those 50's bomb shelters. And the radio looks a lot like this old phone my grandmother had hanging in her laundry room and involves rabbit ears and tin foil. (It's a pretty strange place, my head.)
And what kind of radio is it? Are there like anarchists broadcasting secret shows that only these amateur radio operators can hear? Or is it like a big CB radio, so all these people are talking to truckers? And, really, what's the point? Is it like a club or some subculture like barbershop quartet people? How many of you know that my very first boyfriend was in a barbershop quartet with his dad? I went to a couple of competitions and let me tell you that is an interesting subculture. It involved a lot of plaid and a lot of vests, I'll tell you that! But I digress...
Does anyone know anyone that does this? I have a basement now, so should I be getting on this bandwagon? My friend Jessica needs a hobby...should I steer her in this direction?
I know it sounds like I'm making fun (and I guess I am, a little), but I really want to know!