The BW Bars indicator is based on the initial entry level of the "ProfitUnity" approach by Bill Williams, described in the book "Trading Chaos".
It shows the extreme bars on the chart, that is, the bars that opened and closed in the same third of the bar.
"Whenever you see an extreme (a bar that both opens and closes in the same third, top or bottom, of the bar), 85% of the time the market will change direction within the next 1 to 5 bars of the same duration as the bar you are examining. This knowledge alone can change the results of your trading. It is extremely helpful for intraday trading." Bill Williams, Trading Chaos.