For an international audience, "The City" means London's financial district. This is the only use of the term sufficiently common to be mentioned on Wikipedia's article.
I'd say either NY or London is fine for an international audience.
SF, not so much - and I hate, hate, hate how that reference shows the promise of the internet as a world without locality has been lost and turned into California, with the rest of the world as an afterthought.
(Australian here, for reference)