Doorway to Heaven
You've heard the old saying: when life opens a door, take it off its hinges and write all over it to make a sign for your cattle company. Well, that's an adage Gus McCrae lives by, anyway. "He was the only person in Lonesome Dove with enough literary talent to write a sign" (8.25). He uses an old door to create a sign advertising the services of the Cattle Company and displaying the credentials over everyone who works there.
Once he starts, he can't stop writing it. Eventually, the whole door is covered. Gus uses big words no one knows, like "emporium" (8.26), and Latin phrases that even Gus doesn't totally understand. He wants to show off his intelligence. The Latin he carves is this: "Uva uvam vivendo varia fit,which seemed to him to be a beautiful motto, whatever it meant" (8.48).
What it means is "a grape, seeing another grape, changes color" (source). Considering what Clara has to say about Call changing Gus, and vice-versa, this motto is pretty apt.
When the Cattle Company leaves for Montana, Gus brings the sign with them. He considers it his "masterpiece" (96.142). So when Gus is killed, Call takes it all the way back to Texas and uses it as Gus's grave marker. However, during the journey, most of the words are worn off. Call carves Gus's initials in the side of the board. All those words are reduced to only two initials, just as death can reduce someone's life to just the memory of their name.