Hi John,
Here is some theory on the tracking signal. link
Every time a forecast is run, the system compares the tracking limit with the tracking signal, which is calculates internally. The tracking signal is the quotient of the error total and the mean absolute deviation. This comparison helps you control the accuracy of the forecast. If the tracking signal is greater than the tracking limit, the system issues an exception message asking you to check the forecast model.
You can use T-Code MP33 to evaluate this Esception messages and others