Fair value is a concept that seems really good on paper to form trading signals, but in reality, probably doesn't even exist.

After all, at any given moment, the fair value is really just the market value of an asset. The demand and supply come together to form the market value, and that should be the market's equilibrium and that given moment.

I'd say just look at sentiment for starters, if you want to find whether a coin is overvalued or undervalued. If sentiment is bullish and people are FOMOing, then the coin is likely to be extremely overvalued, and vice versa. Finding "fair value" requires a ton of modelling that I don't think casual traders are simply up for.