Custom indicator on TradingChart[]

Mathematica provides facility to add indicators like simplemovingaverage using the below code
“TradingChart[formattedData,“SimpleMovingAverage”]”.
I want to add my custom indicator to TradingChart.
Can any one give me code example of doing that i.e. I want a code example of ‘SimpleMovingAverage’ indicator and apply it to TradingChart so that I can follow the same procedure for my custom indicator.

I just joined this community to ask precisely the same question.