Not in detail or the actual means but you would need to think along the lines of if user is a certain user group and post submitted then use "x" styling option which would probably need you to make you own styling markup for it in EXTRA.css. I haven't thought of or tried this so I can't offer you a method or even guarantee that something like what I said would work. But it is a place for you to start investigating at least
I see Ryan's already done this on Postloop with a special .staff CSS class, but I'm not sure of the exact implementation...just thought I'd let you know it's been done.
{xen:if '{$message.is_admin} OR {$message.is_moderator}', 'staff'}"
I've not ran a check but if you dump the $message variable (probably should wrap it in a conditional or your PHP will probably run out of memory dumping it for every message) you should be able to use $message.node_id.
I see Ryan's already done this on Postloop with a special .staff CSS class, but I'm not sure of the exact implementation...just thought I'd let you know it's been done.