Jimmy Valentine assumed the name of Ralph Spencer when he became a businessman and fell in love with Annabel Adams. He intended to leave his old name behind him along with his criminal past. When he uses his burglar tools to release the little girl trapped in the bank vault, he assumes that he has sacrificed his reformation and everything that went with it, including Annabel.
Jimmy Valentine put on his coat, and walked outside the railings toward the front door. As he went he thought he heard a far-away voice that he once knew call “Ralph!” But he never hesitated.
Jimmy does not answer Annabel because he feels he is no longer Ralph Spencer and that he cannot escape being a thief and a jailbird named Jimmy Valentine. In not answering Annabel's call of "Ralph!", Jimmy is showing that he knows he has lost her irretrievably. But then, in one of O. Henry's famous surprise endings, his reformation is retrieved when Ben Price confronts him and calls him by his adopted name.
“Hello, Ben!” said Jimmy, still with his strange smile. “Got around at last, have you? Well, let's go. I don't know that it makes much difference, now.”
And then Ben Price acted rather strangely.
“Guess you're mistaken, Mr. Spencer,” he said. “Don't believe I recognize you. Your buggy's waiting for you, ain't it?”
The name Ralph Spencer means a lot. It makes the difference between being a crook and an honest citizen. As Ralph Spencer, Jimmy can go back to Annabel and her family and continue the life of an honest citizen and married man. The name Ralph Spencer is symbolic, and it is used effectively by O. Henry in his totally surprising ending.
O. Henry does not state what will become of the suitcase full of burglar tools. Presumably Annabel will forgive and forget his past because of his heroic action, and her father will do the same the same. Getting rid of the burglar tools completely makes a better ending than having Jimmy pass them on to his old friend Bill, who would have used them to crack more safes.