Ohhh, is that what they are supposed to be checking against? I don't think I've never had someone cross check the signatures in my life.
Matter of fact, only one time have I ever had someone alert me that there was no signature on the back of my card (I don't even sign the backs of my cards, woops).
I was in Paris once (I'm a US citizen, for context), and after paying for something the receipt machine printed out a receipt with a signature line on it. The gal behind the counter handed it to me, puzzled. I signed it and handed it back and could tell she was even more puzzled. It was at that point I realized, "What is the point of this signature thing?"