A majority of people have seen magic on television before. Years before I got into magic, I knew that people usually sign the card in the middle.
Wouldn't it be kind of weird if someone said "Sign this coin on the top part." You are basically making them sign a white strip,which psychologically means nothing. When you sign across the spades and actual colored ink, you know your signature is on that card and is not going anywhere. Mentally, it is a huge difference.
Everyone has differing opinions, and this is just mine. I personally don't like the idea of signing in a specific area. And what happens when the spectator accidentally goes out of the white area? Some people have Gs or Ys in their name and the bottoms of these letters will more than likely go into the colored area. Maybe that is not an issue, but I am guessing it would be since he asks the spectator to sign in the top part to begin with.
How often do you perform on the street? Not everyone will gather around and come close. Some people like to stay off to the sides. Even by you asking them to please gather around, a few people will stay lurk around to your sides. Not always, but it will happen. So this might also be an issue for people. It is an issue for me.
Fraud has one item you need to buy and I already had that one as do alot of other people. This has 3 items you need, which a reviewer stated that most people won't have at home. Again, not practical for everyone as some people might not have any art supply stores located near them.
Just my opinion...