I seem to be in the minority here but I personally prefer using $ and # to denote root. I like this because not everyone uses sudo and might not even have it installed.
That being said, if you already have other commands that are using sudo -u … to run commands as a different user then it might be best to just be consistent and prefix everything with it, but if there is only a few of those maybe a # cp foo bar && chown www-data bar is an alternative.