The Linear Regression Trend line approximates real data's pointer could be well described by the R-Squared or R2 indicator. A perfect fit is observed, when an R-Squared is on 1.0 point. However, when the R-Squared goes lower than 1.0 point, it means that there are no relationships between the price and the Linear Regression Trend line.
|Number of Periods||R-Squared Critical Value
When R-Squared rounds off at extreme levels, a Short-term position could be considered opening opposite the prevailing trend. For example, a Short position could be regarded selling or opening, when the slope is positive and 0.80 point is overcame by R-squared then it starts to turn down.
You may find a lot of ways to use the linear regression outputs of R-squared and Slope in trading systems. If you need more information about the R- Squared, read it in the book The New Technical Trader written by Stanley Kroll and Tushar Chande.