Posted By:
T206Collector...you should write "Property of Leon" on the back of all of your blank backed cards. Or, better yet, let me write "My Other Backs Say Sweet Caporal" on the back of all of your blank backed cards. Even if you believe that the monetary value wouldn't diminish, you'd have to concede that the aesthetic value certainly would.
Put another way, writing on the back of a blank backed card cannot possibly enhance the value (unless it's an authentic autograph, I suppose). So the answer is either zero or minus.