Whenever a faster moving average crosses with a slower moving one, it provides a technical signal.  If the faster MA crosses "over" the slower one its bullish, but if it crosses under then its a bearish indicator.

The lower the number of days the faster the moving average....so the 20 DMA moves faster than the 50, the 50 moves faster than the 100 and the 100 moves faster than the 200.  

So in this case the 20 dma is the faster moving average, and with it crossing under (or below, however you want to phrase it) the slower moving 50 DMA....that is absoultely a bearish techincal indication.