I am using nbconvert to produce something as close as possible to a polished journal article.
I have successfully hidden input code using a custom nbconvert templat
%%HTML
This will hide both In and Out prompts
Note that this is only in your browser, the notebook itself isn't modified of course, and nbconvert will work just the same as before.
nbconvert
In case you want this in the nbconverted code as well, just put the in a Raw NBConvert cell.