I think the 'in USD' is essential, otherwise I would think you were talking about 11M BTC.
Exactly.
or 186,929,000 EUR
or etc...
Money Supply = Monetary Base * Money Multiplier
Since BTC lacks any significant fractional reserve the money multiplier is 1. Having M0 and nothing else seems "excessive" like making categories for category sake.
"Oh so the Bitcoin M(0) is xxxx USD, what about the total money supply?" "Yeah that is the same number".
In the proper context, I'm sure if you said Market Cap, Bitcoin Money Supply in USD, or Bitcoin Money Supply, or just Money Supply people would know what you meant. I've used it many times before, myself.
Being specific would be another thing.
I think M0 in USD is the most simple, with the least amount of words/letters, yet most effective and specific way of saying it. Those who don't know what M0 means could be taught something new. Would take a couple seconds to do, no biggie. I think the point of this is to try and promote the use of something like that. Getting away from Market Cap as it's confusing and not very specific.
imho