Ted Warren's "Perfect Sell Signal"

Look at the 1-year price chart for the asset under scrutiny.
If you can identify a recent up trend, mark it on the chart.  It should cover at least half the year.
When the current price breaks down and drops through the up trend, it's time to sell.

Ted Warren wrote a book a long time ago called "How To Make The Stock Market Make Money For You".  This is one of the key take-aways from that book.  Yes, it applies to cryptos - and many (or possibly all) other asset classes as well.