My thoughts is that these signature campaign is obsolete in todays social media world. They can spam telegram, Facebook, email accounts, twitter etc to promote their ICO/airdrop/Bounties.
This forums would be better off with focused discussion on real issues, ideas, Anns etc. People can still earn their bounties in the other arenas. Bitcointalk has been diluted to a point of ridicule. I wholeheartedly agree with OP, but unfortunately I do not have any merit to prove this.
If organizations are still actively paying for signature campaign you can bet they're effective at advertising. People wouldn't pay for an ineffective way to advertise, and IIRC some campaigns in the past even included a link in the signature code so every click would be logged.
Merit itself has partially caused this Meta subforum to absolutely blow up. Discussion between people that have a pulse still happens in most subforums, but less so in subforums like Bitcoin Discussion. I personally would like more moderation in subs like those to eliminate people reiterating the same points over and over again and to prevent signature spammers from copy-pasting and editing their garbage responses there. Ever since Frodocooper was added to the Mining subforum as a mod, spamming has almost ground to a complete halt there (though there
have been times moderation was questionable like in the KNC thread). Moderation might be a bit costly but it's absolutely worth it.