What is the post 2008 monopoly currency symbol called (M with two lines through it) and is there an alt-code for it? Below is an example of it from Monopoly Deal but it is also used in the regular monopoly game post-2008.

What is the post 2008 monopoly currency symbol called (M with two lines through it) and is there an alt-code for it? Below is an example of it from Monopoly Deal but it is also used in the regular monopoly game post-2008.

It is most likely just an imaginary symbol for Monopoly money.
For "everyday use", the closest symbol might be "₩" or "₩", just turned upside down. This is a symbol for Won, currency used in South and North Korea.
Since the Monopoly M is not a real symbol, it does not have an alt-code. It can be still used via LaTex. Dont worry, it's not very hard. Here's an little example.

For those who know Latex already: Use this in your preamble
\usepackage{textcomp} % for the Won symbol
\usepackage{graphicx} % Needed for the rotation
And this to make an alias
\newcommand{\M}{\rotatebox[origin=c]{180}{\textwon}}
You may now use \M to insert the Monopoly M.
For those who are not used to Latex:
Copy-paste this into blank document in Overleaf.com, and edit it for your needs (You will need to sign up, but it is free). Then download your pdf or just use Print Screen, depending on your needs.
\documentclass[a4paper,10pt]{article}
\usepackage[utf8]{inputenc}
\usepackage[english]{babel}
\usepackage{textcomp} % for the Won symbol
\usepackage{graphicx} % Needed for the rotation
\begin{document}
\newcommand{\M}{\rotatebox[origin=c]{180}{\textwon}} % make an alias '\M' for the upside-down Won.
\Large
\underline{\M { }stands for \M onopoly \M oney} \\[20px]
\large
\begin{tabular}{ll}
Fish & \M 100 \\
Chips &\M 50 \\
Fish \& Chips \qquad \qquad & \M 120\\
\end{tabular}\\[20px]
\Large
Normal: \M \qquad Bold: \textbf{\M}
\end{document}
As Wikipedia states, the first symbol (₩, WON SIGN) is at Unicode code point U+20A9, and has HTML code ₩. The second symbol (₩, FULLWIDTH WON SIGN) is at Unicode code point U+FFE6 and has HTML code ₩.
It doesn't appear to have an official name, and the change is somewhat stealthy. The Monopoly wiki says
The Dollar, also called "the Monopoly Dollar", "$", "pound", "£", "munny", and "Monopoly Money", is the main currency used in Monopoly.
The new symbol is mentioned in passing:
In Pogo.com's World Edition, as well as the Here and Now Edition, a new symbol was added, a capital M with 2 horizontal lines in it. This seems to be the accepted symbol for Monopoly money.
I'm guessing the change is to standardise the money for future localised versions of the game, rather than printing e.g. either British pounds or dollars or local_currency_x. The large number of synonyms for the name suggests to me that this has never been given much thought.
Given that it doesn't have a name, it doesn't have an alt-code either.
To answer the question, "What is the post 2008 monopoly currency symbol called (M with two lines through it)", according to the game Monopoly Millionaires and recent online variations, it is called the Monopole.
Well it seems to me that if it resembles the Chinese Won (except upside down of course) wouldn't calling it Mon be a reasonable solution? After all it is very easy to remember even for the younger players.