I think you're mistaken. Signature is usually part of a bounty campaign. The average bounty campaign is usually split into the following: Signature campaign, article writing, youtube videos, twitter retweets & likes, Medium claps, etc. A fixed percentage would be offered to each campaign, and users would receive stakes, and the total tokens allocated for bounty would then be distributed accordingly.
For an airdrop campaign, you could launch it after the bounty campaign, to attract new investors.
Yes signature is part of a bounty campaign, but airdrop is frequently part of a bounty campaign too. By the way, signatures is one of the most profitable bounty tasks unlike airdrop.
Nope,these days developers are starting to reduce the trust from signature campaign to the social media campaigns and article making.because they have learned the spamming this forum has,and investors are not satisfied about the outcome from the forum posting.