Airdrops and bounty campaigns are one of the quick and precise ways to promote new projects by investors, and this is a must for investors, the results to be achieved are also comparable to what they promote.
Signature and airdrop can only do marketing but when it comes to credibility it depends on the kind of transparency and reputation they are projecting and what kind of project, they are building, you can market your project through a signature campaign for a whole year but investors will just ignore it if it does not meet their expectation.
Don't rely on a signature campaign when it comes to credibility.