It's probably from one of your effects. When I make a pop out sig, I place a black background behind it all to make sure I got everything that isnt supposed to be there.. I then switch it to a white background to get any dark spots that shouldnt be there. I definitely love the idea however. I will tell you the same thing I told nugget though, be very selective with your render when doing these types of sigs. You want to try to avoid renders that have their arms or heads cut off at a spot leaving straight lines where their arm should be. I hope that makes sense. Not too bad however.