Of course there are. They're easier to pick out in informal writing, of course, but even, "is capable of writing extensively in SWE without screwing up or revea

Of course there are. They're easier to pick out in informal writing, of course, but even, "is capable of writing extensively in SWE without screwing up or revealing lower-class status through choice of word or idiom" is a pretty strong class marker. One can even infer gender with much better-than-even odds, though, again, it's easier the less-formal the writing. There exist computer programs that attempt that trick with fair success, too, though humans are plenty capable of it on their own. As for your example of mathematicians, and to offer a sense of how easy it can be to accidentally and innocently give these things away, something as simple as preposition use can give away a mathematician (or at least someone who's had some exposure to mathematical writing and usage). Consider: "over", and "in", for example, and also seemingly-innocent usage like the transitive verb "having", in a revealing context. See the commas after the closing quotation marks, in that second paragraph? If I'm American, and not obviously-deficient in the rest of my writing, that's a fairly reliable signal that I'm a programmer.