At the moment the one line of which I think everybody asking a question (for the first) will notice reads "Please read the FAQ and the How to ask a good question page." I can imagine, all the rest might well be ignored by some. But this one, due to its location between the title box and the main box, is hard not to notice.

However, is it clear that this is understood as: 'Dear FirstTimeUser, you would be really well-advised to read these two pages before asking a question.' I'd say the interpretation 'Dear FirstTimeUser, in case you experience technical difficulties in using the site, you can have a look here an there.' is also somewhat possible. (After all there are some buttons over the box to enter text whose meaning might or might not be clear, and what is this Community Wiki check box and so on. But then some people might know all this from other sites, and even if not, well, you basically type in the text and hit the obvious button, so easy enough no need for any reading.) Of course the 'good' gives a hint that this is not only about technicalities but then this might go unnoticed.

Perhaps simply a change of formulation 'What type of questions are apropriate' instead of 'How to ask a good question' would make more explcit what is meant while still being not disrespectful.

Also, there is an SE site for photographers and what little experience I have of it (slightly more than I have of Maths-SX!) is that it is pretty much as an_mo_user describes: its core group consists of motivated amateurs and there are also a group of experts who drop by to help out. Indeed, there is quite a bit of tension on the SE network about sites that try to delimit their scope by level instead of subject: we're often held up as a shining example of a site that places boundaries by level and just as often derided for that. That's incidental to this thread, though anyone who wants to know my opinion can probably guess it and if they're not sure then they can read it: http://www.math.ntnu.no/~stacey/CountingOnMyFingers.

I agree with the premise that it could be made clearer that this is a site for professional mathematics (note: not necessarily professional mathematicians). I don't think a pop-up "Is your question appropriate?" would work for the reasons given above, but underlining somehow the professional nature would actually benefit both sides: those with questions we'd like to discourage will be discouraged because they'll think "What is professional mathematics? I've no idea, so maybe this isn't the site for me." and those we'd like to encourage will be encouraged because they'll think "At last, an internet site for people like me!".

I don't know how to implement this, though, as I don't really look at the site any more (by "look" I mean that I don't take in the visual stuff as I'm so used to it by now. I don't mean that I don't visit any more!).

On the other hand, I think that simoncfr has a point. Todd Trimble says 'analogous professional site dedicated to something like biochemistry' (emphasize mine). What I am a bit dubious about is precisely if everybody understands this professional nature of MO (without reading the FAQs). On the front page it does say 'a site for mathematicians'. But, if I'd see a Q&A site which says 'a site for photographers/gardeners/golfers/fishermen/whatever' (these sites are made up, though some might even exist, no clue) then I actually doubt my first thought would be this is a site almost exclusively for professional photographers/gardeners/golfers/fishermen/whatever, but rather for somehow motivated amateurs in the respective activity where some pros occassional drop by to help with tricky questions. And, it is my impression though I am as said rarely on other Q&A sites, that it is quite exceptional that a site of such a level exists for a subject; but Andrew Stacey has some essay on his website, written for the tex-se site, which makes among others such a point. So, it is not so surprsing that some people are mislead. And, now it said 'biochemistry' and not one of the activities I gave that are more likely to be a hobby. But, here I think we also face the 'problem' (though most of the time it is not such a problem)that we (or at least I, but then there was a thread on 'responses to bad at math' so I guess it is not such a unique experience) face frequently in real life; namely, that by no means all people even know that something like professional mathmatical research exists at all, and among those that do know still most have a completely flawed idea that is, only slightly exagerrating, somehow along the lines 'convoluted calculus problems, hard logic/number puzzles, programming a computer to compute something really long and complicated'. And, more or less these are the question that we are 'complaining' about here. So, what rests for me is somehow the argument that people ought to understand form the other questions that they are wrong here. But, also this is not so clear (even leaving aside the point on this I made before and focusing on the more random sample of newest or active questions). Perhaps it is helpful to think about how easy or not it is for a 1st year undergrad to distinguish what is an assignment for a 3rd year undergrad form what is an ansignment for a beginning grad student from what is research level mathematics.

And of course I do not want to claim it is in anyway hard to find out about the professional nature (well, it suffices to read the FAQs of course), but still I share simoncfr's view that it is at least not obvious, and perhaps could be stressed a bit more. But, how exactly I am not sure, as to overdo it certainly could back-fire. Maybe just a line above the ask box: Please note this site is mainly intended for professional mathematicians, for details please see the FAQs.

And, it is my impression, that there are some users (that seem like reasonable people from what they write and how they react, just not mathematicians) that are honestly surprised when they are told there question is too simple. An easily visible hint regarding the essentially purely professional nature of the site might help. It is true that its says it is a site 'for mathematicians' but perhaps this is not explicit enough. True, writing something like: "if you do not consider yourself as a professional mathematician you are most likely wrong here" might also not be the way to go, but perhaps there is something in between.

The most cursory glance at the neighboring questions should convince anyone that this is a pretty high-level site; if they can't figure that out and behave accordingly, then they are really in the wrong place. My own opinion is that the MO community shouldn't have to go out of its way to explain this.

I did get a chuckle recently when someone told John Baez to take his question to math.stackexchange. Run along now... :-)

I think generally the comments people leave when closing inappropriate questions are not too snobby or elitist. If someone gets offended by "this is not appropriate for this site, please read the FAQ" then, well... would they get offended if they walked into a medical convention and started asking questions about high school biology, then were shown the door?