Back then 0.1BTC is quite easy to earn since bitcoin doesn't cost that much and the signature campaigns aren't that strict yet. But now that a lot of users are here and the price has increased, the payment rate went down and getting 0.1BTC a week is quite hard. However, I know I user that can get 0.1BTC in a week.
This guy (deisik) can make $45.5 a week by not doing anything at all. He's in the coinroll signature campaign and they pay $0.0005 for every post that you have in the past. He's at 13k posts as of today so that's $0.0005 * 13k * 7 = $45.5
And sure enough from how often this guy is online, he's making around 200 posts a week or even more. I'm not really sure. But 200 posts is $0.25 x 200 = $50. That's $95.5 all in all and it keeps increasing as time goes by since the number of post count that he has continue to increase.
You are explain about earning from signature campaign, very well, and also i am impress about your calculation. But instead of it, we could earn from signature campaign when our rank will be legendary. You are right, it is not a topic. Also we could earn 0.1 btc from different ways like altcoin trading.
As a matter of fact, you don't have to be a legendary to earn 0.1BTC in a week. In the same campaign, coinroll, you can earn 0.1BTC in a week but you have to be really really active. 0.1BTC = $100 / $0.25 = 400 posts a week. I think that's doable if you have no life or you have nothing else to do or you are simply motivated enough to develop a discipline that can reach this amount of posts without spamming the whole forum with garbage posts.
There's a guy that posted tons of garbage in this forum while enrolled from that campaign. He was probably hoping to make tons of btc in one week. He got paid several times (I think) but I can't find his account anymore or maybe I don't recall his name anymore.
I think it's alright to post that much (since there's no rule about how much posts you can do per day) but it should all be constructive and should have a good time interval in the posts so you wouldn't be tagged as a spammer.