Henry from Waah is feeling unloved right now because no-one is posting any comments to his blog. So I'll link to his post about credit card signatures, referring to this prank. I can confirm that no-one seem to care about the signature on the credit card slip.
A former boss of mine, a gweilo with a fairly obviously Western name, used to test this out in restaurants. Waiters seemed quite unconcerned when his colleagues who were obviously Chinese signed the credit card slip with a signature that was clearly quite different. They just don't care, apparently.