I would mention domains for sale in your sig and link it to a page with info.
And I wouldn't even discuss it in a thread like this personally. Unless you are posting a killer domain.. people cant seem to help posting how little it's worth to them. And that just makes those who can see value in it, feel like they might look silly for asking a question.
*Edit
and I promise I didn't see Plateman's post before I posted this!