It would be handy to have quick links to other sites when you want to suggest that the question might be better handled there. I know a lot of the abbreviations from the hot questions ribbon, but digging out a link when I need one is a pain. Please use the same abbreviations used in the ribbon.
By quick links, I mean just using the square brackets to trigger the link without having to use parentheses and the address.
I think the feature you want already exists, at least for comments (here's a feature request to bring this syntax to posts too). According to this answer:
[so],[su],[sf],[metase]/[meta.se],[a51],[se]– link to the given site (Stack Overflow, Super User, Server Fault, Meta Stack Exchange, Area 51, the Stack Exchange portal). Link text is the site name.
[something.se]– link to something.stackexchange.com, if that site exists. Link text is the site name. Use[ubuntu.se]for Ask Ubuntu, and[mathoverflow.se]for Math Overflow.To link to a site-specific Meta site, use:
[sitename.meta.se]or[meta.sitename.se].
Using the HNQ site ballon letters would be problematic for several reasons: most graduated sites don't have letters in their icons (e.g. Arqade and Academia), some sites have the same letter(s) used (e.g. Health and History), and the icons don't always use alphanumeric characters (e.g. Hinduism and Chess).
If that doesn't work for you, you can try this userscript.
[ell.se], [interpersonal.se] and [engineering.se].