I've never picked up a signature series book, but the more I look into graded moderns, the more I see this option. Heck, in some instances, there are more SS items in the census than universal.
For the modern collector, are SS books the preferred copy? Is there any rough guidelines that you follow when determining the value of a book that's signed vs. unsigned? For example, for the average, non-hyped book, is the SS version worth 50% more? 30% more? I know it's a case-by-case sort of thing, but does anyone have advice for someone just now looking into such things?