If you work really hard you could easily make .5 from signature campaigns, it would just take a lot of forum time and such you really just have to follow their guidelines and make sure not to mess up. hope this info helps!
Someone obviously can make 0.5btc from a signature campaign and that won't even take that much hard work as earning from a signature campaign is quite the easiest way around, but it would take him a lot of time if he just relies on signature campaign to achieve his target, he should probably try every method he can to save a lot of his time or to earn more then he is expecting in that time.