The Fast Globex Sentiment Index is a great tool for showing the pessimism/optimism of market participants at any given time.

Practically this can be used for trading in several ways:

1. The easiest way to look at it is that when it is showing extreme pessimism price is getting in an area where a bounce could ensue, while if it is showing extreme optimism a correction is close by. However this type of signal should be viewed more as a warning signal to be on the look-out for the aforementioned reactions, rather than a "hard" signal because there are situations in which price could travel a lot further in the direction of the trend, while FGSI is pegged at the lower/upper boundary.
2.  Confirmed lows/highs - when both Sentiment and price action make lower lows or higher highs. This indicates the continuation of the trend.
3. Unconfirmed lows/highs - when price makes a lower low (or higher high), but Sentiment makes a higher low (or lower high). This indicates pause/reversal. These can be extremely powerful, especially when coming after a prolonged move and showing several unconfirmed lows/highs.
4. Excess Energy set-ups -  when Sentiment moves a lot in one direction, but price does not, indicating buyer/seller inefficiency. These can hold, meaning the inefficient side is likely to get rolled over, or fail which can lead to strong reversals (e.g. If excess energy gets broken through this can lead to an acceleration towards that side).