I have seen most of the question without \ce{...}. I don't know why user don't use that. Might be they are not aware about that because it is not used in other S.E.

So how to aware users about it I think best way to make new user aware is, to put that in formatting help box.

• The best way is to edit it in thoroughly and leave a comment under their post, like I did here – Martin - マーチン Sep 3 '14 at 9:05

As far as asking goes, there's a link to MathJax help on the sidebar:

However, it's a bit hidden. In the past, I've found that linking people to that page in comments helps immensely — I used to go around mhchem-ifying posts and then leaving comments to teach the new users how to do it themselves (having an example in front of you helps)

I think the approach that Martin proposes in the comment above is really the most practical:

The best way is to edit it in thoroughly and leave a comment under their post, like I did here

I'm optimistic that our core users can use this "teach a man to fish approach" for most cases.

The editing help (accessible via the golden question mark at the upper right corner of any question or answer textbox, then via "Advanced Help"/"LaTeX")

talks about formatting $\LaTeX$, but it doesn't really go into the mhchem particulars. I think we had talked about getting some more detailed instructions into the editing help, but I think it was decided that we would have a separate page in the site help, which can be found at: https://chemistry.stackexchange.com/help/notation.

We can revisit getting it into the editing help, but I think the above link along with the gentle reminders for new users should do the trick in most cases.

• I wouldn't have noticed the implementation of mhchem, if I wasn't made aware of this via a comment - it is quite hidden. Most users react quite friendly with a "thank you" and start using it for the next questions/ answers. (Only a few are too stubborn, lol.) – Martin - マーチン Sep 9 '14 at 7:38