The chainbb-general tag is used for the General Discussion forum specifically.
Each post you create on chainBB does have a special metatag attached to it, so the steemit.com UI could automatically display where it came from regardless of the tags you use. However, if you're looking for a tag just to let your followers know where the post came from, the general chainbb tag might be good enough. Just don't use it as the first tag :)
Thanks @jesta , now its clarified. I assume the metatags arent something visible to us as users, since they arent 'useful'?
It's not visible on steem, no. It shows here on chainBB though, it's the little label below when it was posted.
chainbb/0.1