After spending lot of time on this issue.I finally found the solution to print double hyphen sign simultaneously in post of Octopress.Octopress uses markdown as a default text editor.In recent time,Octopress come up as a promising bloging platform.I was working on my staging blog which is based on Octopress.
While writing the post in Octopress,I stuck with one issue.At one section in post ,I wrote the keyword --comment. The both — sign changed into en-dash.

To print -- on html page by using markdown. We can use the given below html code
It will print two hyphens(--)

--