[Dudhbbh3343]

Is it? The dollar sign typically refers to USD if not otherwise specified.

I would consider it ambiguous only if used in a Canadian or Australian context. (Or other country that uses $ for their currency).

[Taniwha]

Only in the US, just as the NZ$ is implied in NZ, AUD in Oz etc

Certainly when the local media here reports on how much Donald Trump has to pay they convert from US$ to NZ$

[tsimionescu]

I think in most of the world, $ implies USD unless otherwise specified. The only exception are the few other countries that use dollars, where naturally $ is assumed to mean their local $.