So the answer is: don't trade based on that alone. If you're interested, find some online resource (or probably better: a book) on TA, and you'll probably find moving averages as lines of resistance/support in general, and the the SMA200 in particular covered. But there is no single "magic" indicator signal you can slavically follow. If there would be such an obvious one, it would be broken through use and become unprofitable in no time.