Please don't use "M$"
M$ (Microsoft): used to emphasize the allegation that Microsoft has business practices that focus on making money rather than producing good products or looking after the end user's needs and interests. Microsoft was convicted under United States anti-trust law of taking unfair advantage of its monopoly position. Also criticized for taking advantage of loyal customers and upgrading products annually for an expensive price, thus "shafting" the people who bought last year's products.
I don't see anything wrong with using M$ to imply all of the above in one simple and worldwide recognizable satiric misspelling.
See also, satire
If you'd like to draw attention to Microsoft's illegal behavavior in the market, you have to explicitly state it, a dollar sign won't be enough for most people, who think you might simply be poor and envious.
I would, however content that a company which is focusing on something other than making money for its shareholders is dishonest, as that is what is expected of a for-profit business.