When do you think bitcoin price will start falling?
Nobody knows. What can we only give is a warning.
Observe Bitcoin in the first months of 2021, you will have an idea if when it will start to fall (if it will fall

).
What are the signs to watch out for?
When the supports that you've plotted will be easily taken out then it can be a sign that it is starting to fall.
If you see red candles on the daily chart then it is also a sign.
News might also a sign too but don't rely too much on it. Better rely on technical rather than fundamental.