I know there are tons of meta questions about cross-posting already. This question isn't about the cross-posting etiquette per se. It might just be a personal bias or the questions I tend to click on, but there seems to be more cross-posting to MathOverflow than usual by new users.
My thought is that this is probably due to the fact that more and more people have become aware that both of these sites exist (and the fact that I tend to only click on questions that it is reasonable to post to either site). It makes sense that new users who are aware of both sites that want an answer as fast as possible will just immediately post to both.
Is it at all reasonable to just point out that we are aware of MO existence on the help/faq page and say that if you cross-post to MO to link to it and reference it? It is mildly annoying to try to keep my eye out for this, but it is also the case that I usually catch it and post a link in the comments.