It's very hard to tell. In fact, Dan Smith has proved this here on italki on a couple of occasions. He posted four news reports on the same topic (US, GB, Can, Aus). There were no obvious cultural references, no spelling clues, and because the language was neutral/semi-formal there were no regional colloquialisms. And you know what? We, as native speakers, couldn't really tell which was which. We were left to pick up on clues such as whether or not metric measurements were used ( which is obviously a cultural rather than linguistic issue, anyway).
So, the answer is no : apart from the few minor spelling variations and capitalisation/punctuation conventions, there aren't really any obvious differences in the written language. Informal and conversational written language may include regional slang and colloquialisms, but a newspaper article, business letter or academic text won't. The standard grammar of English is the same wherever the speaker comes from.
In my job, I spend a lot of time looking closely at written texts originating in different parts of the English-speaking world. If there are no obvious spelling clues, I can often read an entire article on science or history without knowing whether the writer is British or American. And when I do find a clue, it's often something quite small, such as whether "likely" is used as an adjective or adverb, whether a collective noun is treated as singular or plural, or the odd irregular verb such as fit/fitted. These are very minor differences which many people wouldn't even be aware of.