I’m really happy to hear that, Norman. I’m glad that your tenacity is starting to bear fruit. 
As to your question:
This particular MA, the 200 period, is famous mainly because of its early beginnings. Its history seems to stretch back to the early development stages of TA in the stock markets. At that time, it was the daily closes that were used and were probably mainly calculated manually using the simple MA formula. So a 200 day MA line would have been considered as an indication and measure of the direction and strength of the underlying annual trend (although 250 days would be maybe closer to an actual year).
In those early days of stock markets, the main participants were not day traders, they were typically the banks, funds and wealthy investors - and all looking to buy and hold as long term investments, there was no CFD/electronic/small retail/ instant pricing/filling/microlot/VPN/ type world in existence.
But a Simple MA is just a mathematical formula which told us what was the average price of the prior 200 daily closes, nothing more. It just showed what the average yearly overall price direction was which could then be compared with where prices actually were “today”.
But in today’s trading world that same graphical representation of the slowly evolving annual changes in the stock market has become applied to every timeframe from daily down to mins, etc. Therefore its initial purpose has evaporated…but its reputation has not!
Therefore such a classic indicator, with an established past record in some form or other, becomes vastly familiar to the millions of traders and other market participants. The impact of this is to focus and concentrate the entire attention of this audience on the specific value of this single MA. The end result is a self-filling limited reaction whenever prices approach these levels - on a daily, 4H, 1H, 15min TF and so on.
Naturally, by sheer definition, in a rising or falling trend, current prices will be leading the MA. So it is predominently true that prices below it are bearish and above it bullish. But that, by itself, does not make this 200-period MA into a trading system.
As the saying goes: “If you don’t know where you are going then all roads will get you there”. In the same way, if one does not know what one is looking for from their trading then how can one interpret what such a longer term MA is be used for. A trend trader may look for one thing whilst a swing trader may look for something else. A day trader is in a different class altogether and a scalper probably would have no interest whatsoever in this MA.
Personally, I do plot this line but I only really use it to help in defining target levels and possible re-entries in longer term trends (although I don’t actually hold positions long term - this level just gives a good definition for a reasonable entry/stoploss level with a healthy R:R ratio.)
In order to try to accelerate and improve accuracy of the signals generated by such an MA, various versions of calculating MAs have been devised such as exponential, weighted, etc which either add greater emphasis to the near term closes and/or incorporate some form of smoothing process such using high/low/close values instead of just the close. But I think that this particular MA is still most commonly used with a simple average of the closing values.
