well i can give you an example of one way its slightly usefull....
the other day i went to charge something at the store and the cashier thought it didnt charge me... and that it was denied.... but it wasnt... so then i went ahead and put it on another card.... so i was basically charged for the same thing TWICE...
Now, when we got the bill we called the credit card company for the first one and told them that it's not valid.. and they have no signature... not even a fake..
So basically noone signed to take the stuff under that credit card.. meaning they cant charge anyone....
