Component/s: Coding style
It looks like we don't use # comments in Moodle code nearly at all, I've found them used in very few places:
60:# 5 minutes past 4am
(and few more)
Let's just add a line to http://docs.moodle.org/dev/Coding_style#Documentation_and_comments that says that those (#) should not be used.
Btw. there is no difference in PHP between # and // - it's only the matter of preference/taste/consistency.