is it on everyone's profile
I think cryptotalk contact some bitcointalk members by pm and asking for add signature. Like signature bounty. If any trust person pm you. obviously you believed that.
Cryptotalk didn't pm any members to join their campaign the application was automated through their yobit exchange. But they had a campaign manager that monitored the participants on the other hand Signature bounties are much different there's less moderation from what i've experienced but maybe that just depends on the manager.
What he means he joined on cryptotalk forum is he registered on cryptotalk forum and then join on their signature campaign on there. Idk what is requirement to join on cryptotalk forum as it's still new forum (but the pay rate is very low compared with on here, which has been closed now).
Their campaign on cryptotalk wasn't clearly specified someone mentioned that the campaign was limited to russian members only and you have to reach the max post count just to receive the payout.