You would be surprised how many people call out thier pin number when putting it in,or they keep a note on a bit of paper,I have even seen people who have written it on the card
then there are the people who kids know thier number or thier friends.Of course the Americans still don't have pin numbers and they rarely sign thier cards either.The best way is to sign the card and write on the card,ask for I.D.
The French are very good at pin numbers as they were converted before us.