A semaphore signal indicator that uses two Moving Averages in the form of NRTR. There is a the channel formed by these Moving Averages. Moving Averages have the same periods of averaging, but one of them is drawn on the basis of high[], the other - on low[] timeseries. The exit beyond the boundaries of this channel gives the signal of change of the trend with the corresponding color. After that, until the opposite signal is appeared, there is the drawing of the NRTR Moving Average corresponding to the trend direction.

This indicator was first implemented in MQL4 and published in Code Base at mql4.com on 23.07.2008.   

Fig.1 The SSL indicator