The “percentage of BTC supply on exchanges” is a metric that tells us the ratio between the exchange reserve and the total supply of the crypto.
When the value of this indicator moves up, it means exchange wallets are receiving a net amount of coins. As investors usually send their coins to exchanges for selling purposes, this supply is often referred to as the sell supply of the market. Therefore, an uptrend in it can be bearish for the price of the crypto.
On the other hand, when the metric’s value moves down, it means holders are withdrawing their Bitcoin from exchanges. Prolonged such trend can imply there is accumulation going on in the market, and the available supply is shrinking. Hence, downwards movement of the indicator can be bullish for BTC.