From stockcharts.com
"MACD generates bullish signals from three main sources:
Positive Divergence
Bullish Moving Average Crossover
Bullish Centerline Crossover"
"A Bullish Centerline Crossover occurs when MACD moves above the zero line and into positive territory. This is a clear indication that momentum has changed from negative to positive, or from bearish to bullish. After a Positive Divergence and Bullish Centerline Crossover, the Bullish Centerline Crossover can act as a confirmation signal. Of the three signals, moving average crossover are probably the second most common signals."
"A Bearish Centerline Crossover occurs when MACD moves below zero and into negative territory. This is a clear indication that momentum has changed from positive to negative, or from bullish to bearish. The centerline crossover can act as an independent signal, or confirm a prior signal such as a moving average crossover or negative divergence. Once MACD crosses into negative territory, momentum, at least for the short term, has turned bearish."
"The significance of the centerline crossover will depend on the previous movements of MACD as well"
And there is plenty more on stockcharts.com and other resources and I can safely assume that none of the above has been copyrighted by any of ET members, what I do is not original, neither it belongs to anybody here on ET.