Actually the signature line on your card is your agreement to the terms 
from the credit card company. A card not signed or with Check ID is not 
a valid card. Any merchant who has bothered to read the entire merchant 
agreement (and chooses to stick to it verbatim) will refuse to take the 
card and in some cases will confinscate the card for the card company.
As a merchant taking cards, I have had people who never signed the card 
(blank) argue that someone stealing the card could just copy their 
signature without even comprehending that someone stealing an unsigned 
card will sign however they want to. I always insisted that someone with 
an unsigned card show me picture ID and sign the card. Any merchant who 
has had a charge back due to non-matching signatures will definately 
check the signature line against the signature panel on the card. I 
would guess that most check out people are not high enough in the 
company to understand the rules that the owner has agreed to with the 
card issuers/processors, has never seen them, doesn't care, or all of 
the above. Reading these contracts is like reading a EULA, most people 
don't read it all.

Tom Achtenberg wrote:

> I have had check ID on my cards for several years and so has my wife.  Neither of us has ever been turned down for a sale because of that.  In fact many cashiers (we both used to cashier at Home Depot) AND bank tellers have complemented us on doing so.
>