It just looks like an arrow pointing down. Seems to general to me.

I disagree. It's looks cool but it's too easy to confuse with a fancy down-pointing arrow. Unless you know you're looking for the 'M', you probably won't notice it.

The problem with this one is that once you make more general by removing embedded effect and make it black and white only, it does not look that good any more.

Personally I like this one the most http://dribbble.com/shots/424394-Markdown - as the dashes are really reminding me Markdown.

improved: more M-ness to balance the arrow-ness and make it more distinctive, and -- more importantly -- made bolder to work at small sizes:

https://plus.google.com/102359018718464872517/posts/LKJA5Uua...