What I've seen in terms of tagging content without attracting undue notice is constructions like #himym for ts, i.e. HIMYM for Tumblr Savior. There's a certain inelegance to the practice, I guess, but as far as I know it more or less works.

(My own Tumblr experience is wholly unmediated by third-party add-ons, which might help explain why I can't seem to use it actively for more than a week or so at a stretch.)