I actually had that set on 5 but it did nothing this is why I thought I might have missed another setting, even on 15 it is not showing anything. As you can see from the screen shot above my other forum works as it should.
As you can see even on the default XF style it is not showing and I do have new media
I assume that it's on by default for members unless they switch it off. No idea if it's disabled for all if the unviewed media count has previously been disabled in the ACP and then re-enabled. I think @Chris D will need to answer this one.
It is on by default, however if it is disabled globally, there's likely a situation where it is set to off for the user if they save their Preferences. I've just made a change (for 1.1) so that their previous preference is remembered in case it is disabled and re-enabled.
In terms of enabling it for everyone:
UPDATE xf_user_option SET xengallery_unviewed_media_count = 1