The thread you made about the Legend of Korra podcast is considered advertising on this forum. Making threads for the sake of getting something more attention, as well as posting to individuals, is considered advertising. The only place you're allowed to advertise stuff is in your signature, so I advise editing something about the podcast into it. In addition, you can also make it known to people in the avatar thread that you've got a podcast going and would like to see if anyone is interested. Just let them know about the plans for a podcast and to contact you by PM. The way I see it, the less wordy a subtle but allowed advertising, the better.