Credit Card Signature Prank

By way of Mefi:
This fella experimented to see just how different you could make the signature on your credit card receipt before anyone notices:

Next time I bought something that required a signature, I considered just creating a rectangle of solid black. Then I thought a grid might be weirder:

Only the most Matrix-obsessed fanboy would actually use a grid for his signature, but the chick at the Cheesecake Factory didn't look twice. I mean, I didn't even have on a trenchcoat.