AFIAK, the hash/she/pound symbol is being used for directives. The only directive mSL has right now is Groups via /enable and /disable, but it pretty much prohibits this character from being used for commenting because any arbitrary string can be used in group names.
#Is_This_A_Comment On
On *:START: echo -a Hello World
#Is_This_A_Comment End
Afraid it would be impossible without first making Groups obsolete.