It is hard to determine if the airdrop you joined is Legit. There are lots of scammer circulating in the internet asking for donations to be able to send you and airdrop the afterwards if they had already got those donations they would just suddenly disappear. We have to check first and foremost the website they have provided and check on the whitepaper as well as the background of the people who controls that particular coin. With that i think it would help a bit to know the identity of the airdrop but of course it would not guaranteed us that it is really legit. We do still need to be careful in joining airdrops.