If "someone else" is referring to the cashier, the customer uses the payment machine themselves. In PIN using countries the waiter brings a machine or you step over to the front counter.
If someone else is your spouse, kid, or personal assistant; you tell them the PIN or ask the issuer for an authorized user card.
Well, you don't. But I wouldn't have a problem with my partner using my card, in which case I just give them my pin? On the other hand, that is(or should be) literally impossible with signature.
I...don't. Ever. Why would you do that? That's terrible.
I usually transfer them the money through the free, instant, secure and traceable inter-bank transfers that are universally provided by every financial institution in my country to every other financial institution in my country, so that they can use their own card.
