I can't believe that there is no answer yet where people could vote for the capital M and lowercase k. This is one.
+1 for international standards here. -1 if you dislike international standards.
Disclaimer: I'm a non-native English speaker and user of SO and SE sites. And perhaps I can speak for some other users who are more familiar with international standards than English or American standards.
Top voted answer
The top voted answer says k is not for kilo but an abbreviation for thousand - I can't find a reference for that argument. It is not mentioned as a abbreviation on Wikipedia. Ok forget Wikipedia - anyone could add anything. Also Oxford dictionary never mentions k as an abbreviation of thousand, just for kilo.
If someone says "I make a hundred k a year", they are clearly not saying they make 100 kilodollars a year.
Why not? That's 8333 USD per month - not far-fetched and exactly what I understand. What number do you have in mind when you read that sentence?
Even in Germany you can say
Ich verdiene 80 k.
And everyone will understand, but not because k is the abbreviation of thousand but k is the abbreviation of kilo and kilo means thousand.
At first, I thought this is my answer, but then
[...] users who are unfamiliar with scientific notation [...]
So, who's that then? In Germany you learn that at school. And as already said, for English speakers, the character is the same, it's just the casing.
We cannot have fractions of votes/rep/views/etc
That's true but not a real argument
29.7m is easier to read than 29.7M
According to which design principle or typographic principle please? I'm willing to discuss this on GD.SE
Let's just use E notation...
Well, that's the difference between international and scientific. I don't want to need a master's degree to visit an SE site.