What are the source of Investors knowing when bearish season begins?

[Kemarit]

From what I've seen, it started around November-December or when we reaches the peak of the bull run, and established a new all time high.

in 2017 - It was December, up to the last week
in 2021 - It was November, but people still thinks that we can reach 6 digit that time

And in 2017, at the start of the New Year, there were already signs that the market has change already, up until March that we confirmed that we are in the bear market.

Same in 2021, by January, there are already signs of bearish market.

So the signs is still the same, you just have to be very quick to notice that shift.