how to show underscores symbol in markdown?

There is also the option to use backticks. This is actually used to refer to mark the text as inline code, but where else would you use underscores right? Besides it is much easier than managing the backslash stuff :)

`my_stock_index`

You just escape it with a backslash: my\_stock\_ticker is what you type to get my_stock_ticker

The syntax seems to work for all markdown parsers. However, php markdown parsers use the numeric character reference _ instead of the actual character in it's output.

The single backslash escape works fine in Jupyter unless you are in an italicized block, in which case, you want to close the italicized block, write the escaped underscore, then start the italicized block again.

_the cookie_\__cutter in italics_