I recently started a game, and a 3.5 feat came up called, I believe, Spell Thematics. It allowed you to customize how your spells look in terms of fluff or flavor, as well as giving you a bonus against people trying to figure out what spell you cast.
This sounded silly to me as I was under the impression that you could already personalize spells like this (though the bonus might help), but I realized I had nothing to back it up. Was I just dealing with a GM's personal decision before or is there some rule on personalizing spells?