MACD Indications

Here's how traders take MACD as trading indicators. From the maths of MACD,
MACD = EMA [12] - EMA[26]
Signal = EMA [9] of MACD
A bullish signal (buy in signal) is triggered whenever
A positive MACD (12-day EMA is trading above the 26-day EMA, EMA[12] > EMA[26])
Moving average positive crossover (MACD is trading above the EMA[9] of MACD)
Center line positive crossover (MACD=0 and MACD is trading above the EMA[9] of MACD)
A bearish signal (sell off signal) is triggered whenever
A negative MACD (12-day EMA is trading below the 26-day EMA, EMA[12] < EMA[26])
Moving average negative crossover (MACD is trading below the EMA[9] of MACD)
Center line negative crossover (MACD=0 and MACD is trading below the EMA[9] of MACD)
MACD is more than just about market momentum, it also gives the signal in the trend indication.
If MACD is positive and rising, then the gap between the 12-day EMA and the 26-day EMA will be widening. This indicates that the rate-of-change of the faster moving average is higher than the rate-of-change for the slower moving average. Positive momentum is increasing and this would be considered bullish. If MACD is negative and declining further, then the negative gap between the faster moving average and the slower moving average will be expanding. Downward momentum is accelerating and this would be considered bearish.
Often in reality, the Forex exchange price may drop to new selloff low but the MACD does not hit the new low, this maybe the sign of end of bearish. Or vise versa, the Forex exchange price may hit new high but the MACD might not be hitting on the new high point, this often indicates the change of trend from bullish to bearish.