Public/Private Tags for People I Follow

I'd love it if I could create categories or tags for each tweet that I follow, then I could turn device off/on per tag, or view on the web by tag - and, if I could see other people's tags, I'd be more able to find new info of interest to me (ie, see all of a person's tweets they follow under the tag 'politics' - to see if I discover some new politics info to follow). Tags could be made private or public.