I feel like there's a lack of clear understanding or common usage of many terms related to airdrops, for clarity and from my understanding:
Airdrop = free coins given for zero or near zero effort (ex: providing an address for delivery via PM or form) these may require a signup or occur from holding the coins in the right place during distribution (see:gbyte or bitcore)
Signature campaign= NOT an airdrop, coins given for having a particular sig/avatar to advertise the coin
Bounty= an activity performed to receive coins of a non-trivial nature (ex: writing posts on social media, translating ANNs)
Faucets= free coins given in small (near trivial) amounts for click throughs on a webpage, usually with a catcha and time limit between claims
Fork = free coins generated when an existing coin chain splits and develops independent consensus (see: eth classic or bitcoin cash)
Split/snapshot= a planned distribution of new free coins taken from a single timestamp view of an existing coin chain but generally new coins are completely unrelated to original chain (see:zen or helium)
Exchange/transfer: when an existing coin decides to start a new chain, usually with tech that can't be readily forked, so existing coins are allowed to be cashed in for the new ones, usually over a limited time (see:espers, coinonat)
I'm probably missing other scenarios but I hope to provide some clarity to avoid the muddling of these terms that happens constantly.
Yes, a lot of people mixed up airdrop with signature campaign. And sometimes coin developer also take the word "Airdrop" to attract people to their "signature campaign".