查到壹篇文章才長知識了（原文請見文末）。這篇文章談到，羅馬數字的M代表「千」，而MM代表「百萬」。所以，該文章確實是指30「百萬」。
然後又心想，原來這裏的M不是「百萬」，那下次看到M不就無法知道這到底是「千」、還是「百萬」？剛好這篇文章下面也有提到，很多商業文章會以小寫k代表「千」，而以小寫m（或小寫mn）代表「百萬」，因此得解。
整理在下方供參考：
1. 大寫M：千
2. 大寫MM：百萬
3. 小寫k：千
4. 小寫m/mn：百萬
以下為該文章全文：/blog/what-does-m-and-mm-stand-for
What does M and MM stand for?
The Roman numeral M is often used to indicate one thousand, and MM is used to indicate one million. For example, an expense of $60,000 might appear as $60M. Sales of $3,000,000 might be written as $3MM. Internet advertisers are familiar with CPM which is the cost per thousand impressions.
In recent years some people began using k to represent one thousand. For example, an annual salary of $60,000 might appear as $60k instead of $60M.
In a recent business publication I saw million represented by mn and also by m (both lower case). This means it is possible for you to see $1,400,000 expressed as $1.4 million or $1.4mn or $1.4m or $1.4MM or $1,400k or $1,400M.