That's me, I want to know!
If you got selected for a campaign you may be offered something between 70 to 80$ or maybe more depending upon the campaign.
Some campaigns may pay you even less like 50$ per week or so. Even you may get a lot of worthless tokens in you join bounties for signature space.
I think you should know your price. By the way, what's the purpose of this?
If he wants to rent his signature space, then there is no need to find the price of the signature space as no one will hire him. Only people give offers for signature spaces to people who are highly reputed on bitcointalk. Majority of the posters need to be hired in the campaign first in order to get paid for their signature space.