When Jimmy was a Naval officer in the 1940s, he used the abbreviation for his love. He tells People what those five letters mean, "I love you the goodest. That's what my mother and daddy used to say back and forth, and I picked it up with Rosa."
The message took off with his family, as he says, "Now all our children do the same thing—ILYTG on the phone or in emails. They generally just put the initials." But even Jimmy is not safe from acronym confusion, "And sometimes they change the initials and make you guess what they're talking about."