Not quite 20 years ago, I thought that Einstuerzende Neubauten's "Kein Bestandtiel Sein" really fit a description of things I shouldn't be doing anymore.
So, I paid someone to write it on my neck where it's reminded me of these things every single morning in a mirror, except it's backwards there. But, it's cool, because I know what it says. I mean, sure I could've written it backwards on me, but that would've made it that much more sillier than anything else.
Since it's provided a creedo to live by ("To be no part of it"), plus it's indelible marking on me, I think it qualifies as a "theme song" in its way.