Over a couple of years, just by posting on the forum actually :) Been a member there since 2013 and in those early says it wasn't unheard of to earn a couple of BTC here and there.

Nowadays you have to put a lot more effort in though, just to rank up there. If you get to Legendary rank, that would basically earn you up to 200 dollars per week, just by writing 25 - 30 posts or so.

Check out this page of all the signature campaigns, all the earnings are included:
https://bitcointalk.org/index.php?topic=615953.0

If people are interested I could write a full guide on how to get those kinds of earnings, starting from scratch. If you can write decent enough English, it's no problem at all to grow on that forum.

The 30k is just a rough estimate, including everything I've earned on the forum itself and through offers that I've received via the forum.