It would be nice to do a Search or try out some WQL without creating a new card. A first pass is to include Advanced Search at the bottom of any card you know you might want that - and/or in *sidebar.

The next step would be to throw a little cue text around it and make it available in the footer of every page (width makes this more useable than sidebar) - this might go well with Ethan's idea about card footers.

And the last step would of course be to put a GUI on it.

Somewhere in there we want to add the ability exclude star cards from search results.