And in many places M stands for thousand, from Latin "mille" (as well as the Roman numeral). That doesn't keep people from counting in kilo-, mega- and gigadollars. Still less confusing than dealing with short vs long scale numbers in translation.

I wouldn't immediately parse that abbreviation in the US--but if I did I'd parse it as G being shorthand for grand. More commonly 2Gs would be used for 2x the normal force of gravity--i.e. you weigh twice as much.