Community Quick Filters

I'd like to be able to tag (privately) the communities I've joined, so I can look them up/filter them by those tags. This would also be beneficial in other UI elements, such as when creating a post and needing to select which community to post to.

Along these lines, I'd also like to quickly filter on communities I'm a mod in. I can see there's a "badge" next to those, but there's no way to explicitly filter in these UI elements.