This is a good question. I'll list some things I've attempted to use to solve this, but must admit, it's been with limited success. If you find an accurate way, let me know. I've looked at
time of day/time of year
Volume
The classic higher highs higher lows
Volatility bands (Bollinger, Keltner)
All of them have their good points and their bad. But in the end, I came back to two things. The first is just eyeballing it, and the second is finding a method for which you don't need to always be right about whether it is trending or mean reverting to come out of it ok.
