can Xthreads do this?

[ZiNgA BuRgA]

I'm not sure I get you.
If a forum is closed, MyBB will display a lock icon as well.

If you're referring to custom icons, but not the type that appear beside the status icon, I think there's a mod to do that.
You could theoretically do it through XThreads, but it wouldn't look nice - in fact, Template Conditionals probably does it better (if you can't find a mod which does it already).