Fair Market Value of airdrop coins appears to be taxable as income in USA. It is also relevant to the cost basis for capital gains in the future. I don't see any indication that there was a market for Decred on 2016 February 8, so I am tempted to consider the value to be $0. Can anyone point to an authoritative answer?
This report (https://www.algopulse.io/articles/irs-says-untraded-tokens-are-tax-free) seems to indicate that untraded crypto can be valued at $0. But it's not totally clear.
Although there doesn't seem to be any way to trade Decred before 2016 February 13, coinfairvalue (https://www.coinfairvalue.com/coins/decred/) shows prices and fair values around $1 that may be relevant to February 8, or maybe to February 10.